The exit status of a command

From Linux Shell Scripting Tutorial - A Beginner's handbook
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Each Linux command returns a status when it terminates normally or abnormally. You can use command exit status in the shell script to display an error message or take some sort of action. For example, if tar command is unsuccessful, it returns a code which tells the shell script to send an e-mail to sys admin.

Exit Status

  • Every Linux command executed by the shell script or user, has an exit status.
  • The exit status is an integer number.
  • The Linux man pages stats the exit statuses of each command.
  • 0 exit status means the command was successful without any errors.
  • A non-zero (1-255 values) exit status means command was failure.
  • You can use special shell variable called ? to get the exit status of the previously executed command. To print ? variable use the echo command:

<syntaxhighlight lang="bash" >echo $? date # run date command echo $? # print exit status foobar123 # not a valid command echo $? # print exit status</source>

How Do I See Exit Status Of The Command?

Type the following command: <syntaxhighlight lang="bash" >date</source> To view exist status of date command, enter: <syntaxhighlight lang="bash" >echo $?</source> Sample Output:


Try non-existence command <syntaxhighlight lang="bash" >date1 echo $? ls /eeteec echo $?</source> Sample Output:


According to ls man page - exit status is 0 if OK, 1 if minor problems, 2 if serious trouble.

How Do I Store Exit Status Of The Command In a Shell Variable?

Assign $? to a shell variable: <syntaxhighlight lang="bash" >ls -l /tmp status=$? echo "ls command exit stats - $status"</source>

Exit Status Shell Script Example

A simple shell script to locate username ( <syntaxhighlight lang="bash" >#!/bin/bash

  1. set var


  1. get user name

read -p "Enter a user name : " username

  1. try to locate username in in /etc/passwd

grep "^$username" $PASSWD_FILE > /dev/null

  1. store exit status of grep
  2. if found grep will return 0 exit stauts
  3. if not found, grep will return a nonzero exit stauts


if test $status -eq 0 then echo "User '$username' found in $PASSWD_FILE file." else echo "User '$username' not found in $PASSWD_FILE file." fi</source> Save and close the file. Run it as follows: <syntaxhighlight lang="bash" >chmod +x ./</source> Sample Outputs:

Enter a user name : vivek
User 'vivek' found in /etc/passwd file.

Run it again: <syntaxhighlight lang="bash" >chmod +x ./</source> Sample Outputs:

Enter a user name : tommy
User 'tommy' not found in /etc/passwd file.

You can combine the grep and if command in a single statement as follows: <syntaxhighlight lang="bash" >if grep "^$username:" /etc/passwd >/dev/null then echo "User '$username' found in $PASSWD_FILE file." else echo "User '$username' not found in $PASSWD_FILE file." fi</source> Notice that standard output from grep command is ignored by sending it to /dev/null. ← Multilevel if-then-elseHomeConditional execution →