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in bash regarding "if" condition. How can I write in a script that will check if a text file is empty continue the script else < perform some command>?

John Kugelman
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Alex Zarankin
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  • https://www.gnu.org/software/bash/manual/html_node/Conditional-Constructs.html – Shawn Oct 14 '22 at 10:53
  • In the shell, don't think of it as "if condition". It is "if command". If the command succeeds (returns 0), then do something. The syntax is straightforward: `if cmd; then cmd; else cmd; fi`. Each command can be a block. eg `if cmd1; cmd2; cmd3 && cmd4; cmd5 | cmd6; then cmd7; cmd8; fi`. (In that case, `cmd7 and cmd8` are executed if `cmd6` returns 0.) – William Pursell Oct 14 '22 at 11:25
  • what the command to check whether text file is empty so continue the script and if the file contains strings perform certain command? – Alex Zarankin Oct 14 '22 at 11:35
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    `if test -s file; then echo file exists and is non-empty; fi` and `if grep -q pattern file; then echo file contains pattern; fi` – William Pursell Oct 14 '22 at 11:52

1 Answers1

0

You probably want to this:

if  [ -s "$file" ]
then
    echo 'file exist and non-empty'
    # perform some command then exit?
fi

The [ is a short-hand for the command test. See the man bash in the "SHELL BUILTIN COMMANDS" for details. man test is what I end up using most of the time, though.

If it is important that it is a text file, then preferably check the file has the expected extension (here .txt):

if [ "${file: -4}" = ".txt" ]
then
   echo file is a text file (extension)
fi

"${file: -4} means extract the last 4 letters from the variable file, and we then compare that with ".txt".

Failing that you use the file utility to inspect the content of the file:

if [ "`file -b "$file"`" = "ASCII text" ]
then
   echo file is a text file (content)
fi
Allan Wind
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