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Accepted
Bulrush
Asked: 2015-02-06 05:41:12 +0800 CST

How to see if no output from `ls *.xls` command?

  • 772

Ubuntu 14.04.1.

I have a bash script, called by cron every 10 minutes, which basically looks for files in a subdir, then loops through and process each file. But how do I check if there are no files found? If there are no files found I don't want to process them, and I don't want to get an email via cron that says "no files found", because cron runs every 10 minutes. That's 144 emails per day saying "no files found" that I don't want to get.

  • The input/ dir is owned by me and has full rwx permissions.
  • I've already guaranteed the files in input/ do not contain spaces, thanks to another answer on Ask Ubuntu.

Here's my basic script. 

#!/bin/bash
# Cron requires a full path in $myfullpath
myfullpath=/home/comp/progdir
files=`ls $myfullpath/input/fedex*.xlsx`
# How do I check for no files found here and exit without generating a cron email?
for fullfile in $files
do

done

Thanks! I didn't even know what to google for this one.

EDIT: My script is now this: 

#!/bin/bash
# Script: gocronloop, Feb 5, 2015
# Cron requires a full path to the file.
mydir=/home/comp/perl/gilson/jimv/fedex
cd $mydir/input
# First remove spaces from filesnames in input/
find -name "* *" -type f | rename 's/ /-/g'
cd $mydir
shopt -s nullglob
if [ $? -ne 0 ]; then
    echo "ERROR in shopt"
    exit 1
fi
for fullfile in "$mydir"/input/fedex*.xlsx
    do
    # First remove file extension to get full path and base filename.
    myfile=`echo "$fullfile"|cut -d'.' -f1`
    echo -e "\nDoing $myfile..."
    # Convert file from xlsx to xls.
    ssconvert $myfile.xlsx $myfile.xls
    # Now check status in $?
    if [ $? -ne 0 ]; then
        echo "ERROR in ssconvert"
        exit 1
    fi
    perl $1 $mydir/fedex.pl -input:$mydir/$myfile.xls -progdir:$mydir 
    done
bash

7 Answers

  1. Best Answer

    First things first: Don't parse ls.

    Now that we have got that out of the way, use globbing, alongwith nullglob:

    shopt -s nullglob
for fullfile in "$myfullpath"/input/fedex*.xlsx
do
#.......
done

    Usually with globbing, if * doesn't match anything it's left as is. With nullglob, it is replaced with nothing, so a false match isn't triggered.

    For example:

    $ bash -c 'a=(foo/*); echo ${a[@]}'
foo/*
$ bash -c 'shopt -s nullglob; a=(foo/*); echo ${a[@]}'

$
    • 9

  2. If you're dead-set on using ls anyway, despite it's unsuitability for your original code, or if you:

    just want to find out if ls didn't find any files

    you could check it's exit code. A "No such file..." will fail (exit code 2). While even an empty directory's ls will succeed (exit code 0):

    $ ls *.xls
ls: cannot access *.xls: No such file or directory
$ echo $?
2

$ ls
$ echo $?
0
    • 2

  3. Python seems a comfortable option as well if I am not missing the point:

    #!/usr/bin/env python3
import subprocess
import os

myfullpath = "/home/jacob/Bureaublad" 
files = [f for f in os.listdir(myfullpath) if f.endswith(".xlsx")]

for f in files:
    cmd = "gedit"
    subprocess.check_call(["/bin/bash", "-c", cmd])
    • 2

  4. Let find do the hard work for you. Write a script that processes a file passed as the first parameter, then do this in your crontab:

    find /wherever  -iname 'fedex*.xls' -exec your-script "{}" \;

    find will not generate any output if it doesn't find files matching the expression.

    • 2

  5. If you look at https://stackoverflow.com/questions/2937407/test-whether-a-glob-has-any-matches-in-bash, something like that should work:

    cd "$myfullpath/input/"

if test -n "$(shopt -s nullglob; echo fedex*.xlsl)"
then
    for file in fedex*.xlsl
    do 
          fullfile="$myfullpath/input/$file"
          # things
    done 
fi

    ... Look also at http://mywiki.wooledge.org/ParsingLs

    • 1 
  6. $ if ! ls /tmp/*.bla >/dev/null 2>&1 ; then echo "no meat" ; else echo "have a steak" ; fi
no meat
$ touch /tmp/a.bla
$ if ! ls /tmp/*.bla >/dev/null 2>&1 ; then echo "no meat" ; else echo "have a steak" ; fi
have a steak
    • 1

  7. Why not use the find command, putting a single filename on each line: 

    for fullfile in $(find <dir> -name '*.xslx'); do  
# fullfile now contains the full filename, including any spaces  
# process to your heart's content, using double quotes (") around $fullfile to  
#  make sure the spaces are kept intact  
    cp "$fullfile" /new/directory/  
end
    • 0