Bash tips & tricks

· 164 words · 1 minute read

Bash variable with the content of a file 🔗

NTPFILECONTENT=$(cat /etc/chrony.conf)

This will store the ‘\n’ characters as well.

Display bash variable with the content of a file 🔗

echo "${NTPFILECONTENT}"

Beware the quotes

Append content to a bash variable with a new line 🔗

NTPFILECONTENT="${NTPFILECONTENT}"$'\n'"pool ${ntp} iburst"

Create files with heredocs 🔗

cat << EOF > /your/file
mycontent
  even with spaces
EOF

Some details:

  • You can use EOF or whatever you want.
  • The EOF needs to be as it is, no whitespace before it.
  • If you don’t want to interpret variables in the text, use single quotes such as:
cat << 'EOF' > /your/file
...
EOF
  • In a shell script with tabs such as:
#!/usr/bin/env bash

if true ; then
    cat << EOF > /tmp/yourfilehere
my content
EOF
fi

you better use <<- EOF to disable leading tabs to make the code more readable:

#!/usr/bin/env bash

if true ; then
    cat <<- EOF > /tmp/yourfilehere
    mycontent
    EOF
fi

NOTE: You need to use tabs.

References:

bash tips