Linux Bash Script, Single Command But Multiple Lines?

Question

I have the following script I wrote by searching Google, and it backs up my Linux system to an archive:

#!/bin/bash
# init

DATE=$(date +20%y%m%d)

tar -cvpzf /share/Recovery/Snapshots/$HOSTNAME_$DATE.tar.gz --exclude=/proc --exclude=/lost+found --exclude=/sys --exclude=/mnt --exclude=/media --exclude=/dev --exclude=/share/Archive /

This works, but I am wondering if I can format the script to show the command over multiple lines, something like this, so it is easy to edit later:

tar -cvpzf /share/Recovery/Snapshots/$HOSTNAME_$DATE.tar.gz 
--exclude=/proc 
--exclude=/lost+found 
--exclude=/sys 
--exclude=/mnt 
--exclude=/media 
--exclude=/dev 
--exclude=/share/Archive 
/

That way it is easier to read and edit later. Is it possible to format a Bash script this way?

Solution 1

All you should need to do is add "\" at the end of each line and it should be good to go.

So yours will look like:

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 \
    /

A Few Shortcuts

(based on your comment update for setting $HOSTNAME)

$HOSTNAME

Two options to set that:

1. Set HOSTNAME

   HOSTNAME=$(hostname)

2. Use command substitution (e.g. $(command))

   So it would look like above. That just makes the command run before using it.

$DATE

Another variable avoided would be easily:

$(hostname)_$(date +%Y%m%d).tar.gz \

$ man date will have the formats for the date options, the above is YYYYmmdd

Solution 2

Use the backslash to continue a command on the next line:

tar -cvpzf /share/Recovery/Snapshots/$HOSTNAME_$DATE.tar.gz \
--exclude=/proc \
--exclude=/lost+found \
--exclude=/sys  \
--exclude=/mnt  \
--exclude=/media  \
--exclude=/dev \
--exclude=/share/Archive \
/

Solution 3

You can use this in bash

PARAMS=(
    -cvpzf /share/Recovery/Snapshots/$HOSTNAME_$DATE.tar.gz 
    --exclude=`enter code here`/proc 
    --exclude=/lost+found 
    --exclude=/sys 
    --exclude=/mnt
    # this is a comment 
    --exclude=/media 
    --exclude=/dev 
    # --exclude=/something
    --exclude=/share/Archive 
    /
)
tar ${PARAMS[@]}

Solution 4

The same command, but with comments for each line, would be:

tar -cvpzf /share/Recovery/Snapshots/$(hostname)_$(date +%Y%m%d).tar.gz `#first comment` \
    --exclude=/proc `#second comment` \
    --exclude=/lost+found `# and so on...` \
    --exclude=/sys \
    --exclude=/mnt \
    --exclude=/media \ 
    --exclude=/dev \
    --exclude=/share/Archive \
    /

Solution 5

Axel Heider provided a good alternative to backslashes. Two notes:

1. The command can be included in the list, and
2. The use of the list should be in double quotes "${PARAMS[@]}", so that any spaces in parameters get preserved.

#!/bin/bash

params=(
    show
    hello,
    world
    "multi word"
)

function show {
    echo --- Showing \""$@"\" as parameters ---
    for i in "$@"; do
        echo i=$i
    done
}

${params[@]}
"${params[@]}"

outputs

$ bash test.sh
--- Showing "hello, world multi word" as parameters ---
i=hello,
i=world
i=multi
i=word
--- Showing "hello, world multi word" as parameters ---
i=hello,
i=world
i=multi word

View more solutions

Comments

[Jay LaCroix]

Thanks guys. One last thing. There seems to be a problem with the file name portion of my script: $HOSTNAME_$DATE.tar.gz When I run the script now, the output file is: 20121120.tar.gz

[nerdwaller]

I went back to update it to make it more useful and get the indentations. I love SU though, by and large.

[nerdwaller]

If you want your actual "hostname" put it in back ticks (the tilde "~" key above tab): /share/Recovery/Snapshots/`hostname`_$DATE.tar.gz

[nerdwaller]

Anytime @JayLaCroix - Welcome to SU!

[andrybak]

It is recommended to use $(command) instead of `command`.

[TheDefinitionist]

This doesn't work for me like eg. in alias ub='source ~/.bash_aliases \ && source $HOME/.bash_aliases \ && echo "aliases updated."';

[Paul]

@TheDefinitionist Sounds like a different problem to this one. Perhaps open a new question?

[SDsolar]

Can I line up the backslashes in a column on the right?

[Paul]

@SDsolar You can use spaces and tabs to line up the slashes.

[Timo]

This works with withspaces as a separator. If I have ssh on the first line and commands on the following lines, I think I need a semicolon as well besides backslash.

[Charlie Parker]

what do you need to do for the last argument do you still need the ``?

[timkay]

Should be tar "${PARAMS[@]}", so that params with spaces get preserved.

[roneo.org]

This technique is not recommended when performances matter: "note that this technique is expensive because it creates a subshell for each of such “inline comments” during execution. It is only suitable if the commands performance or cost is not a problem." Source: systutorials.com/…