In Bash how can I check if a string begins with some value

Question

I would like to check if a string begins with  node  e g   node001   Something like  if    HOST    user      then   echo yes fi   How can I do it correctly     I further need to combine expressions to check if HOST is either  user1  or begins with  node   if       HOST    user1    -o     HOST    node        then echo yes fi   gt   gt   gt  -bash     too many arguments   How can I do it correctly

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if       HOST    user1    -o     HOST    node        then echo yes fi  doesn t work  because all of        and test recognize the same nonrecursive grammar  See section CONDITIONAL EXPRESSIONS on your Bash man page  As an aside  the SUSv3 says  The KornShell-derived conditional command  double bracket       was removed from the shell command language description in an early proposal   Objections were raised that the real problem is misuse of the test command      and putting it into the shell is the wrong way to fix the problem   Instead  proper documentation and a new shell reserved word     are sufficient  Tests that require multiple test operations can be done at the shell level using individual invocations of the test command and shell logicals  rather than using the error-prone -o flag of test   You d need to write it this way  but test doesn t support it  if    HOST    user1 -o  HOST    node     then echo yes fi  test uses   for string equality  and more importantly it doesn t support pattern matching  case   esac has good support for pattern matching  case  HOST in user1 node   echo yes    esac  It has the added benefit that it doesn t depend on Bash  and the syntax is portable  From the Single Unix Specification  The Shell Command Language  case word in        pattern1  compound-list           pattern    pattern        compound-list                pattern    pattern        compound-list  esac

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Adding a tiny bit more syntax detail to Mark Rushakoff s highest rank answer   The expression   HOST    node    Can also be written as    HOST     node     The effect is the same  Just make sure the wildcard is outside the quoted text  If the wildcard is inside the quotes it will be interpreted literally  i e  not as a wildcard

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grep  Forgetting performance  this is POSIX and looks nicer than case solutions   mystr  abcd  if printf   s    mystr    grep -Eq   ab   then   echo matches fi   Explanation    printf   s  to prevent printf from expanding backslash escapes  Bash printf literal verbatim string grep -q prevents echo of matches to stdout  How to check if a file contains a specific string using Bash grep -E enables extended regular expressions  which we need for the

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You can select just the part of the string you want to check   if      HOST 0 4     user     For your follow-up question  you could use an OR   if      HOST     user1      HOST     node

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OP  for both your questions you can use case esac   string  node001  case   string  in   node   echo  found          echo  no node    esac   Second question  case   HOST  in  node   echo  ok     user  echo  ok    esac  case   HOST  in  node  user  echo  ok    esac   Or Bash 4 0  case   HOST  in  user    amp   node   echo  ok    esac

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I prefer the other methods already posted  but some people like to use   case   HOST  in      user1 node                echo  yes                           echo  no    esac   Edit   I ve added your alternates to the case statement above  In your edited version you have too many brackets  It should look like this   if     HOST    user1     HOST    node

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I always try to stick with POSIX sh instead of using Bash extensions  since one of the major points of scripting is portability  besides connecting programs  not replacing them    In sh  there is an easy way to check for an  is-prefix  condition   case  HOST in node         Your code here esac   Given how old  arcane and crufty sh is  and Bash is not the cure  It s more complicated  less consistent and less portable   I d like to point out a very nice functional aspect  While some syntax elements like case are built-in  the resulting constructs are no different than any other job  They can be composed in the same way   if case  HOST in node   true      false   esac  then       Your code here fi   Or even shorter  if case  HOST in node         false   esac  then       Your code here fi   Or even shorter  just to present   as a language element -- but this is bad style now   if   case  HOST in node   false   esac  then       Your code here fi   If you like being explicit  build your own language element   beginswith     case  2 in   1    true      false   esac      Isn t this actually quite nice   if beginswith node   HOST   then       Your code here fi   And since sh is basically only jobs and string-lists  and internally processes  out of which jobs are composed   we can now even do some light functional programming   beginswith     case  2 in   1    true      false   esac    checkresult     if        0    then echo TRUE  else echo FALSE  fi     all         test  1  shift     for i in       do          test   i     return     done    all  beginswith x  x xy xyz   checkresult    Prints TRUE all  beginswith x  x xy abc   checkresult    Prints FALSE   This is elegant  Not that I d advocate using sh for anything serious -- it breaks all too quickly on real world requirements  no lambdas  so we must use strings  But nesting function calls with strings is not possible  pipes are not possible  etc

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I tweaked  markrushakoff s answer to make it a callable function   function yesNo       Prompts user with  1  returns true if response starts with y or Y or is empty string   read -e -p    1  Y n    YN         YN     y       YN     Y       YN               Use it like this     if yesNo  asfd   then echo  true   else echo  false   fi  asfd  Y n  y true    if yesNo  asfd   then echo  true   else echo  false   fi  asfd  Y n  Y true    if yesNo  asfd   then echo  true   else echo  false   fi  asfd  Y n  yes true    if yesNo  asfd   then echo  true   else echo  false   fi  asfd  Y n  true    if yesNo  asfd   then echo  true   else echo  false   fi  asfd  Y n  n false    if yesNo  asfd   then echo  true   else echo  false   fi  asfd  Y n  ddddd false   Here is a more complex version that provides for a specified default value   function toLowerCase     echo   1    tr    upper       lower       function yesNo        1  user prompt      2  default value  assumed to be Y if not specified      Prompts user with  1  using default value of  2  returns true if response starts with y or Y or is empty string    local DEFAULT yes   if     2     then local DEFAULT     toLowerCase   2      fi   if      DEFAULT     y      then     local PROMPT   Y n     else     local PROMPT   y N     fi   read -e -p    1  PROMPT   YN    YN     toLowerCase   YN             YN           amp  amp       PROMPT     Y                YN    y         Use it like this     if yesNo  asfd  n  then echo  true   else echo  false   fi  asfd  y N  false    if yesNo  asfd  n  then echo  true   else echo  false   fi  asfd  y N  y true    if yesNo  asfd  y  then echo  true   else echo  false   fi  asfd  Y n  n false

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Another thing you can do is cat out what you are echoing and pipe with inline cut -c 1-1

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This snippet on the Advanced Bash Scripting Guide says     The    comparison operator behaves differently within a double-brackets   test than within single brackets       a    z         True if  a starts with a  z   wildcard matching       a     z        True if  a is equal to z   literal matching     So you had it nearly correct  you needed double brackets  not single brackets     With regards to your second question  you can write it this way   HOST user1 if      HOST    user1           HOST    node       then     echo yes1 fi  HOST node001 if     HOST    user1           HOST    node       then     echo yes2 fi   Which will echo  yes1 yes2   Bash s if syntax is hard to get used to  IMO

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If you re using a recent version of Bash  v3    I suggest the Bash regex comparison operator     for example   if      HOST      user       then     echo  yes  fi     To match this or that in a regex  use    for example   if      HOST      user    host1     then     echo  yes  fi   Note - this is  proper  regular expression syntax    user  means use and zero-or-more occurrences of r  so use and userrrr will match  user   means user and zero-or-more occurrences of any character  so user1  userX will match   user   means match the pattern user   at the begin of  HOST    If you re not familiar with regular expression syntax  try referring to this resource

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Since   has a meaning in Bash  I got to the following solution   In addition I like better to pack strings with    to overcome spaces  etc   A   sdfs  if      A             then     echo  Skip comment line  fi

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While I find most answers here quite correct  many of them contain unnecessary Bashisms  POSIX parameter expansion gives you all you need        host user         host       and       host node         host         var expr  strips the smallest prefix matching expr from   var  and returns that  Hence if   host  does not start with user  node     host user     host node   is the same as   host    expr allows fnmatch   wildcards  thus   host node    and friends also work

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