Ubuntu – How to read a sh file while it is working but deleted

bashcommand line

In an interview they asked me this question.

There was an sh file that is already running, but it has been deleted since starting the execution.

They want me to find the process and read the file.

I managed to find the process with

ps -ef | grep test.sh

and tried to read it by using

cat /proc/PID/cmdline test.sh

but it says

no such file or directory

I didn't know what I should do next so I had to skip this.

Maybe it was an easy question but that was really a good question for me and I really want to know the answer. Can you guys help?

Best Answer

tail -c +0 -f /proc/{pid}/fd/{fd} > /tmp/file

where {pid} is the id of your process and /tmp/file will have its contents. Use another location and name if you want to preserve it.

{pid} is the id of the process.
{fd} is the file descriptor. lsof should show the fd. lsof is likely also going to show "deleted" on the line so you can grep that too. lsof -nP +L1 will list all files with less than 1 link, a file deleted will have 0. Add a | grep {pid} to search for just your PID.
from dessert: lsof -p 22664 | sed -E '$!d;s/.*\s([0-9]+)[a-z]\s.*/\1/' to just get the fd.
from comments: you can use less, cat or cp too. I grew up on tail :)

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Use the PWD variable, or the pwd command with command substitution:

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As mbiber said, source another file. For example, your config file (say some.config) would be:

var1=val1
var2=val2

And your script could look like:

#! /bin/bash

# Optionally, set default values
# var1="default value for var1"
# var1="default value for var2"

. /path/to/some.config

echo "$var1" "$var2"

The many files in /etc/default usually serve as configuration files for other shell scripts in a similar way. A very common example from posts here is /etc/default/grub. This file is used to set configuration options for GRUB, since grub-mkconfig is a shell script that sources it:

sysconfdir="/etc"
#…
if test -f ${sysconfdir}/default/grub ; then
  . ${sysconfdir}/default/grub
fi

If you really must process configuration of the form:

var1 some value 1
var2 some value 2

Then you could do something like:

while read var value
do
    export "$var"="$value"
done < /path/to/some.config

(You could also do something like eval "$var=$value", but that's riskier than sourcing a script. You could inadvertently break that more easily than a sourced file.)

Best Answer

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