Shell script to check if file exists

Question

I m trying to write a simple script that will tell me if a filename exist in  Temp that starts with the string  Test    For example  I have these files  Test1989 txt Test1990 txt Test1991 txt   Then I just want to echo that a file was found   For example  something like this   file  home edward bank1 fiche Test   if  test -s   file   then      echo  found one  else      echo  found none  fi   But this doesn t work

User · Answer

One liner to check file exist or not -   awk  BEGIN  print getline  lt   file txt   lt  0    File does not exist     File Exists

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One approach       shopt -s nullglob   files   home edward bank1 fiche Test     if        files      -gt 0      then     echo found one   else     echo found none   fi     Explanation    shopt -s nullglob will cause  home edward bank1 fiche Test  to expand to nothing if no file matches that pattern   Without it  it will be left intact           sets up a subshell  preventing shopt -s nullglob from  escaping   files   home edward bank1 fiche Test   puts the file-list in an array named files   Note that this is within the subshell only  files will not be accessible after the subshell exits       files      is the number of elements in this array      Edited to address subsequent question   What if i also need to check that these files have data in them and are not zero byte files     For this version  we need to use -s  as you did in your question   which also tests for the file s existence  so there s no point using shopt -s nullglob anymore  if no file matches the pattern  then -s on the pattern will be false  So  we can write       found nonempty      for file in  home edward bank1 fiche Test    do     if    -s   file       then       found nonempty 1     fi   done   if      found nonempty       then     echo found one   else     echo found none   fi      Here the         is to prevent file and found file from  escaping

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You can do it in one line   ls  home edward bank1 fiche Test   gt  dev null 2 gt  amp 1  amp  amp  echo  found one     echo  found none    To understand what it does you have to decompose the command and have a basic awareness of boolean logic   Directly from bash man page         expression1  amp  amp  expression2      True if both expression1 and expression2 are true  expression1    expression2      True if either expression1 or expression2 is true          In the shell  and in general in unix world   the boolean true is a program that exits with status 0   ls tries to list the pattern  if it succeed  meaning the pattern exists  it exits with status 0  2 otherwise  have a look at ls man page for details    In our case there are actually 3 expressions  for the sake of clarity I will put parenthesis  although they are not needed because  amp  amp  has precedence on        expression1  amp  amp  expression2     expression3   so if expression1 is true  ie  ls found the pattern  it evaluates expression2  which is just an echo and will exit with status 0   In this case expression3 is never evaluate because what s on the left site of    is already true and it would be a waste of resources trying to evaluate what s on the right   Otherwise  if expression1 is false  expression2 is not evaluated but in this case expression3 is

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You have to understand how Unix interprets your input   The standard Unix shell interpolates environment variables  and what are called globs before it passes the parameters to your program  This is a bit different from Windows which makes the program interpret the expansion   Try this      echo     This will echo all the files and directories in your current directory  Before the echo command acts  the shell interpolates the   and expands it  then passes that expanded parameter back to your command  You can see it in action by doing this     set -xv   echo     set  xv   The set -xv turns on xtrace and verbose  Verbose echoes the command as entered  and xtrace echos the command that will be executed  that is  after the shell expansion    Now try this     echo       Note that putting something inside quotes hides the glob expression from the shell  and the shell cannot expand it  Try this     foo  this is the value of foo    echo  foo   echo   foo    echo   foo    Note that the shell can still expand environment variables inside double quotes  but not in single quotes   Now let s look at your statement   file  home edward bank1 fiche Test     The double quotes prevent the shell from expanding the glob expression  so file is equal to the literal home edward bank1 finche Test   Therefore  you need to do this   file  home edward bank1 fiche Test    The lack of quotes  and the introductory slash which is important   will now make file equal to all files that match that expression   There might be more than one    If there are no files  depending upon the shell  and its settings  the shell may simply set file to that literal string anyway   You certainly have the right idea    file  home edward bank1 fiche Test   if  test -s  file     then          echo  found one      else         echo  found none   fi   However  you still might get found none returned if there is more than one file  Instead  you might get an error in your test command because there are too many parameters   One way to get around this might be   if ls  home edward bank1 finche Test   gt   dev null 2 gt  amp 1 then     echo  There is at least one match  maybe more    else     echo  No files found  fi   In this case  I m taking advantage of the exit code of the ls command  If ls finds one file it can access  it returns a zero exit code  If it can t find one matching file  it returns a non-zero exit code  The if command merely executes a command  and then if the command returns a zero  it assumes the if statement as true and executes the if clause  If the command returns a non-zero value  the if statement is assumed to be false  and the else clause  if one is available  is executed   The test command works in a similar fashion  If the test is true  the test command returns a zero  Otherwise  the test command returns a non-zero value  This works great with the if command  In fact  there s an alias to the test command  Try this      ls -li  bin test  bin     The i prints out the inode  The inode is the real ID of the file  Files with the same ID are the same file  You can see that  bin test and  bin   are the same command  This makes the following two commands the same   if test -s  file then     echo  The file exists  fi  if   -s  file   then     echo  The file exists  fi

User · Answer

for entry in   home loc etc     do     if   -s  home loc etc  entry      then        echo   entry File is available     else        echo   entry File is not available  fi done  Hope it helps

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The following script will help u to go to a process if that script exist in a specified variable   cat  gt  waitfor csh         bin csh      while    -e  1        sleep 10m      end  ctrl D   here -e is for working with files    1 is a shell variable    sleep for 10 minutes  u can execute the script by   waitfor csh   temp   echo  the file exits

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Wildcards aren t expanded inside quoted strings  And when wildcard is expanded  it s returned unchanged if there are no matches  it doesn t expand into an empty string  Try   output    ls home edward bank1 fiche Test  2 gt  dev null   if   -n   output    then echo  Found one  else echo  Found none  fi   If the wildcard expanded to filenames  ls will list them on stdout  otherwise it will print an error on stderr  and nothing on stdout  The contents of stdout are assigned to output   if   -n   output    tests whether  output contains anything   Another way to write this would be   if     ls home edward bank1 fiche Test  2 gt  dev null   wc -l  -gt 0

[shell] Shell script to check if file exists

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