Shell Script: Echo to Stderr

To distinguish between normal output messages and error messages, sometimes there is a need to write messages to the stderr stream from a shell script. By default, output messages are written to stdout stream only.

To write or echo to stderr, I normally use a custom function that redirects the output of the echo command to the standard error stream.

#!/bin/sh

# call this function to write to stderr
echo_stderr ()
{
    echo "$@" >&2
}

# write to stdout
echo this is stdout

#write to stderr
echo_stderr this is stderr

#!/bin/sh

# call this function to write to stderr

echo_stderr ()

{

echo "$@" >&2

}

# write to stdout

echo this is stdout

#write to stderr

echo_stderr this is stderr

The above script has a custom function called echo_stderr that performs the stderr redirect.

Let’s name the above script as stderr.sh. Based on the script, if you want to filter out stderr messages, perform a redirect like this.

$ stderr.sh 2>/dev/null
this is stdout

1 2	$ stderr.sh 2>/dev/null this is stdout

To filter out stdout messages, perform a similar redirection, but this time by redirecting the stdout stream to the null device.

$ stderr.sh 1>/dev/null
this is stderr

1 2	$ stderr.sh 1>/dev/null this is stderr

Mohamed Ibrahim

ibrahim = { interested_in(unix, linux, android, open_source, reverse_engineering); coding(c, shell, php, python, java, javascript, nodejs, react); plays_on(xbox, ps4); linux_desktop_user(true); }