Linux Bash Scripting: How to modify the ls command output using pr command

I have received the below question in our "Ask a question" section of this blog.

Q: Using set -A write a script to print the output of the ls command in 5 columns with two spaces between each column. Pretend that ls does not have multi column output.

Normally we will get a multi column output if we use the command ls -A as shown below.

/home/sittik/programs $ ls -A arr.sh bigchess.sh chess.sh com file fileread.sh gcom lbigchess.sh loops samp

To print the output of the ls command in five columns with two spaces between each column. You can use the following command.

ls -A | pr -a5 -S" " -T

The pr utility is a printing and pagination filter for text files.

From the man page,

-COLUMN, --columns=COLUMN

output COLUMN columns and print columns down, unless -a is used. Balance number of lines in the columns on each page.

-a, --across

print columns across rather than down, used together with -COLUMN 

-SSTRING, --sep-string[=STRING]

separate columns by STRING, without -S: Default separator <TAB> with -J and <space> otherwise (same as -S" "), no effect on column options

-T, --omit-pagination

omit page headers and trailers, eliminate any pagination by form feeds set in input files

The output of the command would be,

/home/sittik/programs $ ls -A | pr -a5 -S" " -T arr.sh bigchess.sh chess.sh com file fileread.sh gcom lbigchess.sh loops samp setting .setting.swp

suppose if you want to have delimiter as :::: instead of spaces, then you can change the delimiter in the following command.

/home/sittik/programs $ ls -A | pr -5 -S"::::" -T arr.sh ::::com ::::gcom ::::loops ::::setting bigchess.sh::::file ::::lbigchess.s::::samp ::::.setting.sw chess.sh ::::fileread.sh

you can see the difference in the order in which the files are displayed from the above two commands. That is because I purposely did not use -a option to show the difference.

To pretend that ls does not have a multi column output, you need to add the above command as the alias to the ls command as below.

alias ls='ls -A | pr -a5 -S" " -T'

After adding alias, if you use the ls command, you will get the desired output.

/home/sittik/programs $ ls arr.sh bigchess.sh chess.sh com file fileread.sh gcom lbigchess.sh loops samp setting .setting.swp