Multiple line commands (Bash)

There are multiple ways to split a command across multiple lines.

With backslash

Example [1]:

tar -cvpzf /share/Recovery/Snapshots/$(hostname)_$(date +%Y%m%d).tar.gz \
    --exclude=/proc \
    --exclude=/lost+found \
    --exclude=/sys \
    --exclude=/mnt \
    --exclude=/media \ 
    --exclude=/dev \
    --exclude=/share/Archive \

You can align the backslashes. E.g.:

tar -cvpzf /share/Recovery/Snapshots/$(hostname)_$(date +%Y%m%d).tar.gz \
    --exclude=/proc          \
    --exclude=/lost+found    \
    --exclude=/sys           \
    --exclude=/mnt           \
    --exclude=/media         \ 
    --exclude=/dev           \
    --exclude=/share/Archive \

With parameter array

As an example: Command wp help post meta patch update can be rewritten as follows. Note that the opening "(" has on the first line:

params=(
   help
   post
   meta
   patch
   update
)

echo ${params[@]}

wp "${params[@]}"

or even including the command:

params=(
   wp
   help
   post
   meta
   patch
   update
)

echo ${params[@]}

("${params[@]}")

Strings with long texts

How to assign a long text to a string in a practical way?

Subvariables

i0="Jantje zag eens pruimen hangen "
i1="Oh als eieren zo groot. "
i2="De tuinman zag zijn bolle wangen "
i3="Sloeg de vuile gapper dood."

i=$i0$i1$i2$i3

echo $i

Incremental variable

Shorter than above and with full control over lines:

i="Jantje zag eens pruimen hangen "
i+="Oh als eieren zo groot. "
i+="De tuinman zag zijn bolle wangen "
i+="Sloeg de vuile gapper dood."

echo $i

As a multi-line literal

i="Jantje zag eens pruimen hangen,
   oh als eieren zo groot.
   De tuinman zag zijn bolle wangen,
   sloeg de vuile gapper dood."

echo $i

Output:

Jantje zag eens pruimen hangen, oh als eieren zo groot. De tuinman zag zijn bolle wangen, sloeg de vuile gapper dood.

I use this approach quite often, but I somehow feel that it's messy
Under certain conditions (e.g., writing an Apache virtual host file, \n is an escape for newline, but not always

Param array

i=(
   Jantje zag eens pruimen hangen,
   oh als eieren zo groot.
   De tuinman zag zijn bolle wangen,
   sloeg de vuile gapper dood.
)

echo ${i[@]}

With output:

Jantje zag eens pruimen hangen, oh als appelen zo groot. De tuinman zag zijn bolle wangen, sloeg de vuile gapper dood.

The individual lines are treated as cells in the array
Outputting the whole array through [@] strings all cells together, separated by a space
It's pervious to identation - Handy!
How to include whitespace (tabs, enter)?

Example: Multiple conditions in tests

if [[ ${site_array[$i,tag]} =~ "_bal_" ]] && \
   [[ ${site_array[$i,tag]} =~ "_cb_" ]]   && \
   [[ ${site_array[$i,tag]} =~ "_dvb8_" ]] && \
   [[ ${site_array[$i,language]} =~ "en" ]]
then
    ...
fi

Sources