Linux shell output - Handle StdOut

The linux shell/bash terminal default behaviour is print output to the terminal (StdOut : Standard output). But sometimes we need to change this behaviour like save toi a file, display noting ... Here some exaple of user case.

Print output to a file (log.txt)

Example : Save ping outout to a file.

ping -c 4 drupal.org > log.txt

So this command will create a file log.txt contains:

PING drupal.org (151.101.1.175) 56(84) bytes of data.

64 bytes from 151.101.1.175: icmp_seq=1 ttl=60 time=28.8 ms

64 bytes from 151.101.1.175: icmp_seq=2 ttl=60 time=77.0 ms

64 bytes from 151.101.1.175: icmp_seq=3 ttl=60 time=48.3 ms

64 bytes from 151.101.1.175: icmp_seq=4 ttl=60 time=16.5 ms

--- drupal.org ping statistics ---

4 packets transmitted, 4 received, 0% packet loss, time 3003ms

rtt min/avg/max/mdev = 16.521/42.689/77.006/22.838 ms

Print shell script output to a file (From terminal)

Script (test.sh):

#!/bin/bash

date; # This will print the date

Command

./test.sh > log.txt

This will display nothis on terminal, but print the date in to the file log.txt, like:

Fri Jun 16 11:14:27 CEST 2017

Redirect all outputs to a file

To print all outputs of the terminal in to a file, just type exec > THE_FILE_NAME

Example:

exec > log.txt

echo "Just test"

date

... ...

Not print the result, just execute the command

Example: run script but print to nothing.

# Out to nothing

./test.sh > /dev/null

Print a command output to a file and print to the terminal (stdout)

Example:

[COMMAND]| tee [OUTPUT_FILE]

date |& tee log.txt

Print a script output to a file and print to the terminal, from terminal

Examples:

test.sh 2>&1 | tee log.txt

# Or

bash test.sh 2>&1 | tee log.txt

Print a script output to a file and print to the terminal, from the script.

Script :

#!/bin/bash

#

# Test script

exec >  >(tee -ia log.txt)

# OR

# exec 2> >(tee -ia log.txt >&2)

#

# commands to run.

date;

ping -c 4 drupal.org;

Command :

./test.sh