CODEWITHSUNDEEP
linuxbashshellcommand-line-arguments
reectrix
reectrix

Reputation: 8629

If else in xargs

I want to compare the output of tail -1 to see if it's an empty string. For instance, if I am searching for a file with find, and I want to compare the result to "" (empty string), how do I do that? I have:

find . -name "*.pdf" | tail -1 | xargs -L1 bash -c 'if [$1 == ""] then echo "Empty"; else 
< echo $1; fi'

Basically, it will print out the file name if it's not empty, and will print "Empty" if there are no pdf files found by 'find'.

I've tried a number of different variations with using the if-else statements inside a single command, and nothing seems to work.

Upvotes: 1

Views: 4772

Answers (5)

Boop
Boop

Reputation: 1386

With xargs you can use the option --no-run-if-empty.

--no-run-if-empty

-r

If the standard input does not contain any nonblanks, do not run the command. Normally, the command is run once even if there is no input. This option is a GNU extension.

My use case exemple:

find /iDontExist | xargs du -sc
# produce the command `du -sc` on the current directory
# that wasn't the initial aim

A way to avoid this:

find /iDontExist | xargs --no-run-if-empty du -sc

hth

Upvotes: 2

AnotherDeveloperNamedGreg
AnotherDeveloperNamedGreg

Reputation: 567

You could make a script:

#!/bin/bash
output=$(find . -name *.pdf)
if [ -z $output ]; then
    echo "Empty"
fi

Upvotes: 0

konsolebox
konsolebox

Reputation: 75548

You can use a function instead.

function tailx {
    if read -r LINE; then
        (
            echo "$LINE"
            while read -r LINE; do
                echo "$LINE"
            done
        ) | command tail "$@"
    else
        echo "Empty."
    fi
}

You can place that in ~/.profile or ~/.bashrc. Run exec bash -l to reload your bash and run find . -name "*.pdf" | tailx -1. You can also customize that to become a shell script placed /usr/local/bin as /usr/local/bin/tailx instead. Just add tailx "$@" at the end of the script, and add the shell header at the beginning.

#!/bin/bash
...
tailx "$@"

Upvotes: 1

Liz Bennett
Liz Bennett

Reputation: 871

Try this:

find . -name "*.pdf" | xargs -L1 bash -c 'if [ -s $0 ] ; then echo "$0"; else echo "File empty"; fi'

According to man test -s will check to see if the file size is zero.

Upvotes: 3

devnull
devnull

Reputation: 123608

You don't need to pipe output to tail, xargs, and so on...

Simply say:

(( $(find . -name "*.pdf" | wc -l) == 0)) && echo "Empty"

Upvotes: 1

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