bash echo doesn’t work after grep returns nothing
I know people usually use grep in the Linux command prompt (not scripts). I happened to put grep in the script and ran into a strange situation. If the grep command returns nothing, the next line echo has no effect. Below is the script.
grep "abc" /home/testuser/myapp.log echo "abc"
Is this normal behavior for grep? If yes, why?
It seems that set
-e is enabled in your script.
grep has an exit status of 0 if a row is selected, 1 if no row is selected, and 2 if an error occurs. Note, however, that if -q or –quiet or –silent or –silent is used and a row is selected, the exit status is 0 even if an error occurs. In your case, if
abc is not found in /
grep returns 1.
shell usually executes the next line in the script, echo “
abc" even if
grep returns exit status. However, if
set -e is enabled,
bash will no longer execute any lines in the script.
the bash online help page:
-e Exit immediately if a pipeline (which may consist of a single simple command), a list, or a compound command (see SHELL GRAMMAR above), exits with a non-zero status. The shell does not exit if the command that fails is part of the command list immediately following a while or until keyword, part of the test following the if or elif reserved words, part of any command executed in a && or || list except the command following the final && or ||, any command in a pipeline but the last, or if the command's return value is being inverted with !. If a compound command other than a subshell returns a non-zero status because a command failed while -e was being ignored, the shell does not exit. A trap on ERR, if set, is executed before the shell exits. This option ap‐ plies to the shell environment and each subshell environment separately (see COMMAND EXECUTION ENVIRONMENT above), and may cause subshells to exit before executing all the commands in the subshell. If a compound command or shell function executes in a context where -e is being ignored, none of the commands executed within the compound command or function body will be affected by the -e setting, even if -e is set and a command returns a failure status. If a compound command or shell function sets -e while executing in a con‐ text where -e is ignored, that setting will not have any effect until the compound command or the command con‐ taining the function call completes.