What s a concise way to check that environment variables are set in a Unix shell script

Question

I ve got a few Unix shell scripts where I need to check that certain environment variables are set before I start doing stuff  so I do this sort of thing   if   -z   STATE     then     echo  Need to set STATE      exit 1 fi    if   -z   DEST     then     echo  Need to set DEST      exit 1 fi   which is a lot of typing  Is there a more elegant idiom for checking that a set of environment variables is set   EDIT  I should mention that these variables have no meaningful default value - the script should error out if any are unset

User · Answer

Try this     -z   STATE     amp  amp  echo  Need to set STATE   amp  amp  exit 1

User · Answer

We can write a nice assertion to check a bunch of variables all at once       assert if variables are set  to a non-empty string    if any variable is not set  exit 1  when -f option is set  or return 1 otherwise     Usage  assert var not null  -f  variable       function assert var not null       local fatal var num null 0        1     -f      amp  amp    shift  fatal 1      for var in       do        -z     var       amp  amp        printf   s n   Variable   var  not set   gt  amp 2  amp  amp          num null       done    if   num null  gt  0    then          fatal      amp  amp  exit 1     return 1   fi   return 0     Sample invocation   one 1 two 2 assert var not null one two echo test 1  return code    assert var not null one two three echo test 2  return code    assert var not null -f one two three echo test 3  return code      this code shouldn t execute   Output   test 1  return code 0 Variable  three  not set test 2  return code 1 Variable  three  not set     More such assertions here  https   github com codeforester base blob master lib assertions sh

User · Answer

None of the above solutions worked for my purposes  in part because I checking the environment for an open-ended list of variables that need to be set before starting a lengthy process  I ended up with this   mapfile -t arr  lt  variables txt  EXITCODE 0  for i in    arr      do    ISSET   env   grep    i     wc -l     if      ISSET      0        then       EXITCODE -1       echo  ENV variable  i is required      fi done  exit   EXITCODE

User · Answer

I always used   if    x STATE      x     then echo  Need to set State   exit 1  fi   Not that much more concise  I m afraid   Under CSH you have   STATE

User · Answer

Try this     -z   STATE     amp  amp  echo  Need to set STATE   amp  amp  exit 1

User · Answer

For future people like me  I wanted to go a step forward and parameterize the var name  so I can loop over a variable sized list of variable names      bin bash declare -a vars  NAME GITLAB URL GITLAB TOKEN   for var name in    vars      do   if   -z    eval  echo    var name       then     echo  Missing environment variable  var name      exit 1   fi done

User · Answer

For future people like me  I wanted to go a step forward and parameterize the var name  so I can loop over a variable sized list of variable names      bin bash declare -a vars  NAME GITLAB URL GITLAB TOKEN   for var name in    vars      do   if   -z    eval  echo    var name       then     echo  Missing environment variable  var name      exit 1   fi done

User · Answer

Parameter Expansion The obvious answer is to use one of the special forms of parameter expansion      STATE  quot Need to set STATE quot       DEST   quot Need to set DEST non-empty quot    Or  better  see section on  Position of double quotes  below      quot   STATE Need to set STATE  quot     quot   DEST  Need to set DEST non-empty  quot   The first variant  using just    requires STATE to be set  but STATE  quot  quot   an empty string  is OK     not exactly what you want  but the alternative and older notation  The second variant  using     requires DEST to be set and non-empty  If you supply no message  the shell provides a default message  The   var   construct is portable back to Version 7 UNIX and the Bourne Shell  1978 or thereabouts    The   var    construct is slightly more recent  I think it was in System III UNIX circa 1981  but it may have been in PWB UNIX before that   It is therefore in the Korn Shell  and in the POSIX shells  including specifically Bash  It is usually documented in the shell s man page in a section called Parameter Expansion   For example  the bash manual says     parameter  word   Display Error if Null or Unset   If parameter is null or unset  the expansion of word  or a message to that effect if word is not present  is written to the standard error and the shell  if it is not interactive  exits   Otherwise  the value of parameter is substituted   The Colon Command I should probably add that the colon command simply has its arguments evaluated and then succeeds   It is the original shell comment notation  before     to end of line    For a long time  Bourne shell scripts had a colon as the first character   The C Shell would read a script and use the first character to determine whether it was for the C Shell  a     hash  or the Bourne shell  a     colon    Then the kernel got in on the act and added support for     path to program  and the Bourne shell got     comments  and the colon convention went by the wayside   But if you come across a script that starts with a colon  now you will know why   Position of double quotes blong asked in a comment   Any thoughts on this discussion  https   github com koalaman shellcheck issues 380 issuecomment-145872749  The gist of the discussion is        However  when I shellcheck it  with version 0 4 1   I get this message  In script sh line 13      FOO   quot The environment variable  FOO  must be set and non-empty quot      -- SC2086  Double quote to prevent globbing and word splitting   Any advice on what I should do in this case   The short answer is  quot do as shellcheck suggests quot      quot   STATE Need to set STATE  quot     quot   DEST  Need to set DEST non-empty  quot   To illustrate why  study the following   Note that the   command doesn t echo its arguments  but the shell does evaluate the arguments    We want to see the arguments  so the code below uses printf  quot  s n quot  in place of      mkdir junk   cd junk    gt  abc    gt  def    gt  ghi      x  quot   quot    printf  quot  s n quot    x  You must set x       Careless  not recommended abc def ghi   unset x   printf  quot  s n quot    x  You must set x       Careless  not recommended bash  x  You must set x   printf  quot  s n quot   quot   x  You must set x  quot     Careful  should be used bash  x  You must set x   x  quot   quot    printf  quot  s n quot   quot   x  You must set x  quot     Careful  should be used     printf  quot  s n quot    x   quot You must set x quot      Not quite careful enough abc def ghi   x    printf  quot  s n quot    x   quot You must set x quot      Not quite careful enough bash  x  You must set x   unset x   printf  quot  s n quot    x   quot You must set x quot      Not quite careful enough bash  x  You must set x     Note how the value in  x is expanded to first   and then a list of file names when the overall expression is not in double quotes   This is what shellcheck is recommending should be fixed   I have not verified that it doesn t object to the form where the expression is enclosed in double quotes  but it is a reasonable assumption that it would be OK

User · Answer

The    syntax is pretty neat   if     BLAH    1    then      echo  Exists    else      echo  Does not exist    fi

User · Answer

I always used   if    x STATE      x     then echo  Need to set State   exit 1  fi   Not that much more concise  I m afraid   Under CSH you have   STATE

User · Answer

MyVariable  SomeDefault    If MyVariable is set and not null  it will reset the variable value    nothing happens   Else  MyVariable is set to SomeDefault   The above will attempt to execute   MyVariable   so if you just want to set the variable do   MyVariable   MyVariable  SomeDefault

User · Answer

In my opinion the simplest and most compatible check for    bin sh is   if     MYVAR         then    echo  Does not exist  else    echo  Exists  fi   Again  this is for  bin sh and is compatible also on old Solaris systems

User · Answer

This can be a way too   if  set -u     HOME  2 gt   dev null           http   unstableme blogspot com 2007 02 checks-whether-envvar-is-set-or-not html

User · Answer

Your question is dependent on the shell that you are using   Bourne shell leaves very little in the way of what you re after   BUT     It does work  just about everywhere   Just try and stay away from csh  It was good for the bells and whistles it added  compared the Bourne shell  but it is really creaking now  If you don t believe me  just try and separate out STDERR in csh   -   There are two possibilities here  The example above  namely using     MyVariable  SomeDefault    for the first time you need to refer to  MyVariable  This takes the env  var MyVariable and  if it is currently not set  assigns the value of SomeDefault to the variable for later use   You also have the possibility of     MyVariable -SomeDefault    which just substitutes SomeDefault for the variable where you are using this construct  It doesn t assign the value SomeDefault to the variable  and the value of MyVariable will still be null after this statement is encountered

User · Answer

This can be a way too   if  set -u     HOME  2 gt   dev null           http   unstableme blogspot com 2007 02 checks-whether-envvar-is-set-or-not html

User · Answer

MyVariable  SomeDefault    If MyVariable is set and not null  it will reset the variable value    nothing happens   Else  MyVariable is set to SomeDefault   The above will attempt to execute   MyVariable   so if you just want to set the variable do   MyVariable   MyVariable  SomeDefault

User · Answer

This can be a way too   if  set -u     HOME  2 gt   dev null           http   unstableme blogspot com 2007 02 checks-whether-envvar-is-set-or-not html

User · Answer

Surely the simplest approach is to add the -u switch to the shebang  the line at the top of your script   assuming you   re using bash      bin sh -u  This will cause the script to exit if any unbound variables lurk within

User · Answer

bash 4 2 introduced the -v operator which tests if a name is set to any value  even the empty string     unset a   b    c       -v a     amp  amp  echo  a is set       -v b     amp  amp  echo  b is set  b is set      -v c     amp  amp  echo  c is set  c is set

User · Answer

Your question is dependent on the shell that you are using   Bourne shell leaves very little in the way of what you re after   BUT     It does work  just about everywhere   Just try and stay away from csh  It was good for the bells and whistles it added  compared the Bourne shell  but it is really creaking now  If you don t believe me  just try and separate out STDERR in csh   -   There are two possibilities here  The example above  namely using     MyVariable  SomeDefault    for the first time you need to refer to  MyVariable  This takes the env  var MyVariable and  if it is currently not set  assigns the value of SomeDefault to the variable for later use   You also have the possibility of     MyVariable -SomeDefault    which just substitutes SomeDefault for the variable where you are using this construct  It doesn t assign the value SomeDefault to the variable  and the value of MyVariable will still be null after this statement is encountered

User · Answer

Surely the simplest approach is to add the -u switch to the shebang  the line at the top of your script   assuming you   re using bash      bin sh -u  This will cause the script to exit if any unbound variables lurk within

User · Answer

Parameter Expansion The obvious answer is to use one of the special forms of parameter expansion      STATE  quot Need to set STATE quot       DEST   quot Need to set DEST non-empty quot    Or  better  see section on  Position of double quotes  below      quot   STATE Need to set STATE  quot     quot   DEST  Need to set DEST non-empty  quot   The first variant  using just    requires STATE to be set  but STATE  quot  quot   an empty string  is OK     not exactly what you want  but the alternative and older notation  The second variant  using     requires DEST to be set and non-empty  If you supply no message  the shell provides a default message  The   var   construct is portable back to Version 7 UNIX and the Bourne Shell  1978 or thereabouts    The   var    construct is slightly more recent  I think it was in System III UNIX circa 1981  but it may have been in PWB UNIX before that   It is therefore in the Korn Shell  and in the POSIX shells  including specifically Bash  It is usually documented in the shell s man page in a section called Parameter Expansion   For example  the bash manual says     parameter  word   Display Error if Null or Unset   If parameter is null or unset  the expansion of word  or a message to that effect if word is not present  is written to the standard error and the shell  if it is not interactive  exits   Otherwise  the value of parameter is substituted   The Colon Command I should probably add that the colon command simply has its arguments evaluated and then succeeds   It is the original shell comment notation  before     to end of line    For a long time  Bourne shell scripts had a colon as the first character   The C Shell would read a script and use the first character to determine whether it was for the C Shell  a     hash  or the Bourne shell  a     colon    Then the kernel got in on the act and added support for     path to program  and the Bourne shell got     comments  and the colon convention went by the wayside   But if you come across a script that starts with a colon  now you will know why   Position of double quotes blong asked in a comment   Any thoughts on this discussion  https   github com koalaman shellcheck issues 380 issuecomment-145872749  The gist of the discussion is        However  when I shellcheck it  with version 0 4 1   I get this message  In script sh line 13      FOO   quot The environment variable  FOO  must be set and non-empty quot      -- SC2086  Double quote to prevent globbing and word splitting   Any advice on what I should do in this case   The short answer is  quot do as shellcheck suggests quot      quot   STATE Need to set STATE  quot     quot   DEST  Need to set DEST non-empty  quot   To illustrate why  study the following   Note that the   command doesn t echo its arguments  but the shell does evaluate the arguments    We want to see the arguments  so the code below uses printf  quot  s n quot  in place of      mkdir junk   cd junk    gt  abc    gt  def    gt  ghi      x  quot   quot    printf  quot  s n quot    x  You must set x       Careless  not recommended abc def ghi   unset x   printf  quot  s n quot    x  You must set x       Careless  not recommended bash  x  You must set x   printf  quot  s n quot   quot   x  You must set x  quot     Careful  should be used bash  x  You must set x   x  quot   quot    printf  quot  s n quot   quot   x  You must set x  quot     Careful  should be used     printf  quot  s n quot    x   quot You must set x quot      Not quite careful enough abc def ghi   x    printf  quot  s n quot    x   quot You must set x quot      Not quite careful enough bash  x  You must set x   unset x   printf  quot  s n quot    x   quot You must set x quot      Not quite careful enough bash  x  You must set x     Note how the value in  x is expanded to first   and then a list of file names when the overall expression is not in double quotes   This is what shellcheck is recommending should be fixed   I have not verified that it doesn t object to the form where the expression is enclosed in double quotes  but it is a reasonable assumption that it would be OK

User · Answer

bash 4 2 introduced the -v operator which tests if a name is set to any value  even the empty string     unset a   b    c       -v a     amp  amp  echo  a is set       -v b     amp  amp  echo  b is set  b is set      -v c     amp  amp  echo  c is set  c is set

User · Answer

In my opinion the simplest and most compatible check for    bin sh is   if     MYVAR         then    echo  Does not exist  else    echo  Exists  fi   Again  this is for  bin sh and is compatible also on old Solaris systems

User · Answer

Try this     -z   STATE     amp  amp  echo  Need to set STATE   amp  amp  exit 1

User · Answer

Rather than using external shell scripts I tend to load in functions in my login shell  I use something like this as a helper function to check for environment variables rather than any set variable   is this an env variable        local var   1      if env  grep -q    var   then        return 0     else        return 1     fi

User · Answer

Your question is dependent on the shell that you are using   Bourne shell leaves very little in the way of what you re after   BUT     It does work  just about everywhere   Just try and stay away from csh  It was good for the bells and whistles it added  compared the Bourne shell  but it is really creaking now  If you don t believe me  just try and separate out STDERR in csh   -   There are two possibilities here  The example above  namely using     MyVariable  SomeDefault    for the first time you need to refer to  MyVariable  This takes the env  var MyVariable and  if it is currently not set  assigns the value of SomeDefault to the variable for later use   You also have the possibility of     MyVariable -SomeDefault    which just substitutes SomeDefault for the variable where you are using this construct  It doesn t assign the value SomeDefault to the variable  and the value of MyVariable will still be null after this statement is encountered

User · Answer

MyVariable  SomeDefault    If MyVariable is set and not null  it will reset the variable value    nothing happens   Else  MyVariable is set to SomeDefault   The above will attempt to execute   MyVariable   so if you just want to set the variable do   MyVariable   MyVariable  SomeDefault

User · Answer

Parameter Expansion The obvious answer is to use one of the special forms of parameter expansion      STATE  quot Need to set STATE quot       DEST   quot Need to set DEST non-empty quot    Or  better  see section on  Position of double quotes  below      quot   STATE Need to set STATE  quot     quot   DEST  Need to set DEST non-empty  quot   The first variant  using just    requires STATE to be set  but STATE  quot  quot   an empty string  is OK     not exactly what you want  but the alternative and older notation  The second variant  using     requires DEST to be set and non-empty  If you supply no message  the shell provides a default message  The   var   construct is portable back to Version 7 UNIX and the Bourne Shell  1978 or thereabouts    The   var    construct is slightly more recent  I think it was in System III UNIX circa 1981  but it may have been in PWB UNIX before that   It is therefore in the Korn Shell  and in the POSIX shells  including specifically Bash  It is usually documented in the shell s man page in a section called Parameter Expansion   For example  the bash manual says     parameter  word   Display Error if Null or Unset   If parameter is null or unset  the expansion of word  or a message to that effect if word is not present  is written to the standard error and the shell  if it is not interactive  exits   Otherwise  the value of parameter is substituted   The Colon Command I should probably add that the colon command simply has its arguments evaluated and then succeeds   It is the original shell comment notation  before     to end of line    For a long time  Bourne shell scripts had a colon as the first character   The C Shell would read a script and use the first character to determine whether it was for the C Shell  a     hash  or the Bourne shell  a     colon    Then the kernel got in on the act and added support for     path to program  and the Bourne shell got     comments  and the colon convention went by the wayside   But if you come across a script that starts with a colon  now you will know why   Position of double quotes blong asked in a comment   Any thoughts on this discussion  https   github com koalaman shellcheck issues 380 issuecomment-145872749  The gist of the discussion is        However  when I shellcheck it  with version 0 4 1   I get this message  In script sh line 13      FOO   quot The environment variable  FOO  must be set and non-empty quot      -- SC2086  Double quote to prevent globbing and word splitting   Any advice on what I should do in this case   The short answer is  quot do as shellcheck suggests quot      quot   STATE Need to set STATE  quot     quot   DEST  Need to set DEST non-empty  quot   To illustrate why  study the following   Note that the   command doesn t echo its arguments  but the shell does evaluate the arguments    We want to see the arguments  so the code below uses printf  quot  s n quot  in place of      mkdir junk   cd junk    gt  abc    gt  def    gt  ghi      x  quot   quot    printf  quot  s n quot    x  You must set x       Careless  not recommended abc def ghi   unset x   printf  quot  s n quot    x  You must set x       Careless  not recommended bash  x  You must set x   printf  quot  s n quot   quot   x  You must set x  quot     Careful  should be used bash  x  You must set x   x  quot   quot    printf  quot  s n quot   quot   x  You must set x  quot     Careful  should be used     printf  quot  s n quot    x   quot You must set x quot      Not quite careful enough abc def ghi   x    printf  quot  s n quot    x   quot You must set x quot      Not quite careful enough bash  x  You must set x   unset x   printf  quot  s n quot    x   quot You must set x quot      Not quite careful enough bash  x  You must set x     Note how the value in  x is expanded to first   and then a list of file names when the overall expression is not in double quotes   This is what shellcheck is recommending should be fixed   I have not verified that it doesn t object to the form where the expression is enclosed in double quotes  but it is a reasonable assumption that it would be OK

User · Answer

I always used   if    x STATE      x     then echo  Need to set State   exit 1  fi   Not that much more concise  I m afraid   Under CSH you have   STATE

User · Answer

Your question is dependent on the shell that you are using   Bourne shell leaves very little in the way of what you re after   BUT     It does work  just about everywhere   Just try and stay away from csh  It was good for the bells and whistles it added  compared the Bourne shell  but it is really creaking now  If you don t believe me  just try and separate out STDERR in csh   -   There are two possibilities here  The example above  namely using     MyVariable  SomeDefault    for the first time you need to refer to  MyVariable  This takes the env  var MyVariable and  if it is currently not set  assigns the value of SomeDefault to the variable for later use   You also have the possibility of     MyVariable -SomeDefault    which just substitutes SomeDefault for the variable where you are using this construct  It doesn t assign the value SomeDefault to the variable  and the value of MyVariable will still be null after this statement is encountered

User · Answer

We can write a nice assertion to check a bunch of variables all at once       assert if variables are set  to a non-empty string    if any variable is not set  exit 1  when -f option is set  or return 1 otherwise     Usage  assert var not null  -f  variable       function assert var not null       local fatal var num null 0        1     -f      amp  amp    shift  fatal 1      for var in       do        -z     var       amp  amp        printf   s n   Variable   var  not set   gt  amp 2  amp  amp          num null       done    if   num null  gt  0    then          fatal      amp  amp  exit 1     return 1   fi   return 0     Sample invocation   one 1 two 2 assert var not null one two echo test 1  return code    assert var not null one two three echo test 2  return code    assert var not null -f one two three echo test 3  return code      this code shouldn t execute   Output   test 1  return code 0 Variable  three  not set test 2  return code 1 Variable  three  not set     More such assertions here  https   github com codeforester base blob master lib assertions sh

User · Answer

The    syntax is pretty neat   if     BLAH    1    then      echo  Exists    else      echo  Does not exist    fi

User · Answer

MyVariable  SomeDefault    If MyVariable is set and not null  it will reset the variable value    nothing happens   Else  MyVariable is set to SomeDefault   The above will attempt to execute   MyVariable   so if you just want to set the variable do   MyVariable   MyVariable  SomeDefault

User · Answer

This can be a way too   if  set -u     HOME  2 gt   dev null           http   unstableme blogspot com 2007 02 checks-whether-envvar-is-set-or-not html

User · Answer

Rather than using external shell scripts I tend to load in functions in my login shell  I use something like this as a helper function to check for environment variables rather than any set variable   is this an env variable        local var   1      if env  grep -q    var   then        return 0     else        return 1     fi

User · Answer

Parameter Expansion The obvious answer is to use one of the special forms of parameter expansion      STATE  quot Need to set STATE quot       DEST   quot Need to set DEST non-empty quot    Or  better  see section on  Position of double quotes  below      quot   STATE Need to set STATE  quot     quot   DEST  Need to set DEST non-empty  quot   The first variant  using just    requires STATE to be set  but STATE  quot  quot   an empty string  is OK     not exactly what you want  but the alternative and older notation  The second variant  using     requires DEST to be set and non-empty  If you supply no message  the shell provides a default message  The   var   construct is portable back to Version 7 UNIX and the Bourne Shell  1978 or thereabouts    The   var    construct is slightly more recent  I think it was in System III UNIX circa 1981  but it may have been in PWB UNIX before that   It is therefore in the Korn Shell  and in the POSIX shells  including specifically Bash  It is usually documented in the shell s man page in a section called Parameter Expansion   For example  the bash manual says     parameter  word   Display Error if Null or Unset   If parameter is null or unset  the expansion of word  or a message to that effect if word is not present  is written to the standard error and the shell  if it is not interactive  exits   Otherwise  the value of parameter is substituted   The Colon Command I should probably add that the colon command simply has its arguments evaluated and then succeeds   It is the original shell comment notation  before     to end of line    For a long time  Bourne shell scripts had a colon as the first character   The C Shell would read a script and use the first character to determine whether it was for the C Shell  a     hash  or the Bourne shell  a     colon    Then the kernel got in on the act and added support for     path to program  and the Bourne shell got     comments  and the colon convention went by the wayside   But if you come across a script that starts with a colon  now you will know why   Position of double quotes blong asked in a comment   Any thoughts on this discussion  https   github com koalaman shellcheck issues 380 issuecomment-145872749  The gist of the discussion is        However  when I shellcheck it  with version 0 4 1   I get this message  In script sh line 13      FOO   quot The environment variable  FOO  must be set and non-empty quot      -- SC2086  Double quote to prevent globbing and word splitting   Any advice on what I should do in this case   The short answer is  quot do as shellcheck suggests quot      quot   STATE Need to set STATE  quot     quot   DEST  Need to set DEST non-empty  quot   To illustrate why  study the following   Note that the   command doesn t echo its arguments  but the shell does evaluate the arguments    We want to see the arguments  so the code below uses printf  quot  s n quot  in place of      mkdir junk   cd junk    gt  abc    gt  def    gt  ghi      x  quot   quot    printf  quot  s n quot    x  You must set x       Careless  not recommended abc def ghi   unset x   printf  quot  s n quot    x  You must set x       Careless  not recommended bash  x  You must set x   printf  quot  s n quot   quot   x  You must set x  quot     Careful  should be used bash  x  You must set x   x  quot   quot    printf  quot  s n quot   quot   x  You must set x  quot     Careful  should be used     printf  quot  s n quot    x   quot You must set x quot      Not quite careful enough abc def ghi   x    printf  quot  s n quot    x   quot You must set x quot      Not quite careful enough bash  x  You must set x   unset x   printf  quot  s n quot    x   quot You must set x quot      Not quite careful enough bash  x  You must set x     Note how the value in  x is expanded to first   and then a list of file names when the overall expression is not in double quotes   This is what shellcheck is recommending should be fixed   I have not verified that it doesn t object to the form where the expression is enclosed in double quotes  but it is a reasonable assumption that it would be OK

User · Answer

None of the above solutions worked for my purposes  in part because I checking the environment for an open-ended list of variables that need to be set before starting a lengthy process  I ended up with this   mapfile -t arr  lt  variables txt  EXITCODE 0  for i in    arr      do    ISSET   env   grep    i     wc -l     if      ISSET      0        then       EXITCODE -1       echo  ENV variable  i is required      fi done  exit   EXITCODE

User · Answer

I always used   if    x STATE      x     then echo  Need to set State   exit 1  fi   Not that much more concise  I m afraid   Under CSH you have   STATE

User · Answer

Try this     -z   STATE     amp  amp  echo  Need to set STATE   amp  amp  exit 1

[bash] What's a concise way to check that environment variables are set in a Unix shell script?

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