Shell Scripting to Compress directory

Question

$1 is file / folder that want to compressed
Output filename is the same name, plus current date and ext
if output name exist, then just give warning

Example:

./cmp.sh /home/user

It will be /home/user to /home/user_2018-03-11.tar.bz2

i already have lead, but i'm stuck

#!/bin/bash

if ["$1" == ""]; then
echo "Help : To compress file use argument with directory"
exit 0
fi


if [[ -f "$1" || -d "$1" ]]; then
tar -cvjSf $1"_"$(date '+%d-%m-%y').tar.bz2 $1
fi

but the output is _22-04-2018.tar.bz2

Is the problem the missing spaces? `if ["$1" == ""]; then` should be `if [ "$1" == "" ]; then` — user000001, Apr 22 '18 at 09:22
sorry the first if is just help command for something like (-?) — Davin Dirgantara, Apr 22 '18 at 09:24
*"... but i'm stuck"* is not a good problem statement. You need to explain the problem or state the errors. Also see [How to use Shellcheck](https://github.com/koalaman/shellcheck), [How to debug a bash script?](https://unix.stackexchange.com/q/155551/56041) (U&L.SE), [How to debug a bash script?](https://stackoverflow.com/q/951336/608639) (SO), [How to debug bash script?](https://askubuntu.com/q/21136) (AskU), [Debugging Bash scripts](http://tldp.org/LDP/Bash-Beginners-Guide/html/sect_02_03.html), etc. — jww, Apr 22 '18 at 12:14
Possible duplicate of [Shell spacing in square brackets](https://stackoverflow.com/q/19032680/608639), [What's the difference between [ and [[ in Bash?](https://stackoverflow.com/q/3427872/608639), [How to use double or single brackets, parentheses, curly braces](https://stackoverflow.com/q/2188199/608639), [How to check if a variable is set in Bash?](https://stackoverflow.com/q/19032680/608639), etc. — jww, Apr 22 '18 at 12:19

ghoti · Accepted Answer · 2018-04-22T11:59:23.213

I see that you're using quotes to avoid the problem the underscore getting used as part of the variable name. So while $1 is a positional paramater, $1_ is a variable that you have not set in your script. You can avoid this issue by using curly braces, like ${1}. Anything inside the braces is part of the variable name, so ${1}_ works. This notation would be preferable to $1"_" which leaves a user-provided variable outside of quotes. (Of course, "$1"_ would do the job as wel.)

Also, it's probably safer to set the filename in a variable, then use that for all your needs:

#!/bin/bash

if [ -z "$1" ]; then
  echo "Help : To compress file use argument with directory"
  exit 0
fi

filename="${1}_$(date '+%F').tar.bz2"

if [ -e "$filename" ]; then
  echo "WARNING: file exists: $filename" >&2
else
  tar -cvjSf "$filename" "$@"
fi

Changes:

you need spaces around your square brackets in an if condition,
while you can test for equivalence to a null string, -z is cleaner, though you could also test for [ $# -eq 0 ], counting the parameters provided,
using $filename makes sure that your test and your tar will always use the same name, even if the script runs over midnight, and is way more readable,
variables should always be quoted.

Also, are you sure about the -S option for tar? On my system, that option extracts sparse files, and is only useful in conjunction with -x.

ALSO, I should note that as I've rewritten it, there's nothing in this script which is specific to bash, and it should be portable to POSIX shells as well (ash/dash/etc). Bash is great, but it's not universal, and if through your learning journey you can learn both, it will give you useful skills across multiple operating systems and environments.

Much Appreciated for your answer @ghoti, do you know any good books for basic scripting so i can have strong fundamental first ? — Davin Dirgantara, Apr 22 '18 at 09:50
@DavinDirgantara, my pleasure. I'm afraid I can't help much with printed book recommendations, other than to say that anything from O'Reilly is likely to be good. But read everything at [GreyCat's wiki](https://mywiki.wooledge.org/) and don't take tdlp.org as gospel. Ask lots of questions! We love questions! :-) — ghoti, Apr 22 '18 at 09:56

score 1 · Answer 2 · answered Apr 22 '18 at 09:34

1

Use -z switch to check if blank

#!/bin/bash 
if [[ -z "$1" ]]; then 
  echo "Help : To compress file use argument with directory" 
  exit 0 
fi 
if [[ -f "$1" || -d "$1" ]]; then 
  tar -cvjSf $1"_"$(date '+%d-%m-%y').tar.bz2 $1 
fi

answered Apr 22 '18 at 09:34

Mesar ali

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Shell Scripting to Compress directory

2 Answers2