Linux if device exists

One liner to check for file exists [duplicate]

Objective: Check for presence of backup .tgz file containing today’s date; output 1 for OK, 0 for no file. I’m a sucker for one liners 🙂 For example in PHP (and pretty much similar in Javascript), in various scenarios I like to do something like

Is there similar syntax in Bash? I know how to check for presence of a regular file using -f FILENAME, I only want the command to print 1 or 0 🙂

Why isn’t -f enough then? That already returns 0 or 1. Do you want the 0 or 1 to be printed or returned?

@DavDav «I’m a sucker for one liners» You do not need a line break after at the end of a PHP program.

7 Answers 7

#to check if it's a regular file [ -f "/you/file.file" ] && echo 1 || echo 0 #to check if a file exist [ -e "/you/file.file" ] && echo 1 || echo 0 

In shell this charater [ means test, -e if file exists ] end of test && if command return true execute the command after, || if command return false execute command after.
This should work in shell and bash

if [ ! -f /tmp/foo.txt ]; then echo "File not found!"; else echo "file found"; fi 

It should be noted (since the type of person asking a question like this might not think about it) that -f will only alert you of the existence of files you are allowed to see. If you don’t have sufficient permissions on a directory, you can’t see files within it, even if you specify the full path of the file.

Thanks for input — I am aware of this. In the specific case at hand, the user running the script has sufficient permissions in the particular folder.

With zsh :

Would output the number of files in the current directory whose name contains the current date in YYYY-mm-dd format and end in .tgz as a decimal number. Replace (DN) with (DN[1]) if you want only 0 or 1.

To use as the condition in an if statement, you can do:

if ()(($#)) *"$(date +%Y-%m-%d)"*.tgz(DN); then echo found else echo none found fi 

In bash

(shopt -s nullglob dotglob; set -- *"$(date +%Y-%m-%d)"*.tgz; echo "$#") 

(replace «$#» with «$(($#>0))» to get 0 or 1).

if (shopt -s nullglob dotglob; set -- *"$(date +%Y-%m-%d)"*.tgz; (($#))); then echo found else echo none found fi 

With ksh93 :

(FIGNORE='@(.|..)'; set -- ~(N)*"$(date +%Y-%m-%d)"*.tgz; echo "$#") 

if (FIGNORE='@(.|..)'; set -- ~(N)*"$(date +%Y-%m-%d)"*.tgz; (("$#"))); then. 

POSIXly

ls -qA | grep -c "$(date +%Y-%m-%d).*\.tgz$" 

ls -qA | grep -q "$(date +%Y-%m-%d).*\.tgz$"; echo "$(($? == 0))" 

if ls -qA | grep -q "$(date +%Y-%m-%d).*\.tgz$"; then. 

Though the common wisdom is not to parse the output of ls , here with -q , we’re making sure there’s one file per line and the replacing of non-printable characters with ? shouldn’t affect the grep ing for our pattern so it should be relatively safe.

You may see differences if the file names contain sequences of bytes that don’t form valid characters. One advantage is that you’ll get an error message if the current directory is no readable.

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Linux if device exists

ive written a script to backup my /home to my external drive and write a few details to a log.

but I want to have the code check if the external drive is plugged in, so something in pseudo code like..

do the rsync and write details to log file
>

how could this be done in bash?

you must need to check when the device exist something like:

-f will check if the file exist.

thanks for pointing me in right direction.
but to clarify if anyone looks at this thread for help its
if [ -d /media/disk ] as its checking for a directory not a file

I am happy you solved your problem.

Just mark this thread solved with the «Thread Tools»

Probably better to check in /etc/mtab since that file contains a list of all currently mounted devices. Something along the lines of:

if grep ‘/media/disk’ /etc/mtab > /dev/null 2>&1; then
echo «mounted»
else
echo «not mounted»
fi

Add code to the appropriate sections to do something useful other than echo messages to the screen. Good luck!

if grep ‘/media/disk’ /etc/mtab > /dev/null 2>&1; then
echo «mounted»
else
echo «not mounted»
fi

I have a flash drive that always shows as ‘E441-2317’ and it shows in the «etc/mtab» file when inserted. I want it to mount as «/flash» and so I have the code:

if grep ‘E441-2317’ /etc/mtab > /dev/null 2>&1; then
mkdir /flash
# parsing line
mount $what /flash
fi

What parsing is needed, in the «# parsing line» to get the first string set/portion of «/dev/?» for my flash drive from the grep string you are producing here, assigning it to my $what var?

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Thread: bash script, if device exists

Tea Glorious Tea!

bash script, if device exists

ive written a script to backup my /home to my external drive and write a few details to a log.

but I want to have the code check if the external drive is plugged in, so something in pseudo code like..

do the rsync and write details to log file
>

how could this be done in bash?

Quad Shot of Ubuntu

Re: bash script, if device exists

you must need to check when the device exist something like:

«Never make a calculation until you know the answer.» — Wheeler, Spacetime Physics, pg 60.

Tea Glorious Tea!

Re: bash script, if device exists

thanks for pointing me in right direction.
but to clarify if anyone looks at this thread for help its
if [ -d /media/disk ] as its checking for a directory not a file

Quad Shot of Ubuntu

Re: bash script, if device exists

I am happy you solved your problem.

Just mark this thread solved with the «Thread Tools»

«Never make a calculation until you know the answer.» — Wheeler, Spacetime Physics, pg 60.

Frothy Coffee!

Re: bash script, if device exists

Probably better to check in /etc/mtab since that file contains a list of all currently mounted devices. Something along the lines of:

if grep '/media/disk' /etc/mtab > /dev/null 2>&1; then echo "mounted" else echo "not mounted" fi

Add code to the appropriate sections to do something useful other than echo messages to the screen. Good luck!

Dipped in Ubuntu

Re: bash script, if device exists

I have a flash drive that always shows as ‘E441-2317’ and it shows in the «etc/mtab» file when inserted. I want it to mount as «/flash» and so I have the code:

if grep 'E441-2317' /etc/mtab > /dev/null 2>&1; then mkdir /flash # parsing line mount $what /flash fi

What parsing is needed, in the «# parsing line» to get the first string set/portion of «/dev/?» for my flash drive from the grep string you are producing here, assigning it to my $what var?

Don’t PANIC!

Re: bash script, if device exists

Necromancy. I moved your post here

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