luser-demo08.sh

#!/bin/bash

# This script demonstrates I/O redirection.

# Redirect STDOUT to a file.
FILE="/tmp/data"
head -n1 /etc/passwd > ${FILE}

# Redirect STDIN to a program.
read LINE < ${FILE}
echo "LINE contains: ${LINE}"

# Redirect STDOUT to a file, overwriting the file.
head -n3 /etc/passwd > ${FILE}
echo
echo "Contents of ${FILE}:"
cat ${FILE}

# Redirect STDOUT to a file, appending to the file.
echo "${RANDOM} ${RANDOM}" >> ${FILE}
echo "${RANDOM} ${RANDOM}" >> ${FILE}
echo
echo "Contents of ${FILE}:"
cat ${FILE}

# Redirect STDIN to a program, using FD 0.
read LINE 0< ${FILE}
echo
echo "LINE contains: ${LINE}"

# Redirect STDOUT to a file using FD 1, overwriting the file.
head -n3 /etc/passwd 1> ${FILE}
echo
echo "Contents of ${FILE}:"
cat ${FILE}

# Redirect STDERR to a file using FD 2.
ERR_FILE="/tmp/data.err"
head -n3 /etc/passwd /fakefile 2> ${ERR_FILE}
echo
echo "Contents of ${ERR_FILE}:"
cat ${ERR_FILE}

# Redirect STDOUT and STDERR to a file.
head -n3 /etc/passwd /fakefile &> ${FILE}
echo
echo "Contents of ${FILE}:"
cat ${FILE}

# Redirect STDOUT and STDERR through a pipe.
echo
head -n3 /etc/passwd /fakefile |& cat -n

# Send output to STDERR
echo "This is STDERR!" >&2

# Discard STDOUT
echo
echo "Discarding STDOUT:"
head -n3 /etc/passwd /fakefile > /dev/null

# Discard STDERR
echo
echo "Discarding STDERR:"
head -n3 /etc/passwd /fakefile 2> /dev/null

# Discard STDOUT and STDERR
echo
echo "Discarding STDOUT and STDERR:"
head -n3 /etc/passwd /fakefile &> /dev/null

# Clean up
rm ${FILE} ${ERR_FILE} &> /dev/null