Linux – 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.

Typically, 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 /home/testuser/myapp.log, grep returns 1.

The bash

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.

From 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.