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32 questions linked to/from When would you use an additional file descriptor?
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346 votes
8 answers
355k views

While running a script, I want to create a temporary file in /tmp directory. After execution of that script, that will be cleaned by that script. How to do that in shell script?
Bhuvanesh's user avatar
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290 votes
10 answers
220k views

There are some commands which filter or act on input, and then pass it along as output, I think usually to stdout - but some commands will just take the stdin and do whatever they do with it, and ...
cwd's user avatar
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170 votes
12 answers
166k views

I am using ffmpeg to get the meta info of an audio clip. But I am unable to grep it. $ ffmpeg -i 01-Daemon.mp3 |grep -i Duration FFmpeg version SVN-r15261, Copyright (c) 2000-2008 Fabrice ...
Andrew-Dufresne's user avatar
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190 votes
8 answers
222k views

As a comment in I'm confused as to why "| true" in a makefile has the same effect as "|| true" user cjm wrote: Another reason to avoid | true is that if the command produced ...
Kit Sunde's user avatar
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116 votes
5 answers
148k views

eval and exec are both built in commands of bash(1) that execute commands. I also see exec has a few options but is that the only difference? What happens to their context?
Willian Paixao's user avatar
  • 2,761
111 votes
4 answers
136k views

I saw this line in a script: DEVICE=`dialog --inputbox "Festplatten-Laufzeit auslesen. Gebe Sie das gewünschte Device an: " 0 70 "" 3>&1 1>&2 2>&3` What is 3>&1 1>&...
jsterr's user avatar
  • 1,381
107 votes
4 answers
151k views

It seems that normal practice would put the setting of IFS outside the while loop in order to not repeat setting it for each iteration... Is this just a habitual "monkey see, monkey do" style, as it ...
Peter.O's user avatar
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95 votes
2 answers
190k views

Consider the following (slightly silly) script name 'test1.sh': #/bin/bash # sleep 10 & echo sleep pid = $! pkill sleep When I run it, I get not only the output of the echo, but bash's reporting ...
fearless_fool's user avatar
  • 1,115
38 votes
5 answers
123k views

I wanted to know if there is any way of reading from two input files in a nested while loop one line at a time. For example, lets say I have two files FileA and FileB. FileA: [jaypal:~/Temp] cat ...
jaypal singh's user avatar
  • 1,622
58 votes
3 answers
32k views

I want to see the output of a command in the terminal as if there was no redirection. Also, stderr needs to be redirected to err.log and stdout needs to be redirected to stdout.log. It would be nice ...
balki's user avatar
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38 votes
4 answers
52k views

I'm trying to read a text file and do something with each line, using a bash script. So, I have a list that looks like this: server1 server2 server3 server4 I thought I could loop over this using a ...
Kenny Rasschaert's user avatar
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43 votes
2 answers
62k views

I am having a very hard time understanding how does one use file descriptors in shell scripts. I know the basics such as exec 5 > /tmp/foo So fd 5 is attached to foo for writing. exec 6 < /...
Ricko M's user avatar
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11 votes
4 answers
15k views

I am working on a bash script that I would like to work for several types of VCS. I am thinking of testing if a directory is a repo for a system by running a typical info command and checking the ...
Niall Murphy's user avatar
  • 305
11 votes
4 answers
1k views

When trying to redirect program output with the "some number greater than" syntax (eg foo 2> myfile), what are the possible numbers here and what do they represent? I believe 1 is /dev/stdout, 2 ...
Fermat's Little Student's user avatar
  • 585
12 votes
3 answers
18k views

How can one measure individual calls to bash functions from inside the bash file. I have a program that I call using the command eclipse -b col_solve.pl -e "myPred" This call outputs some ...
ZakC's user avatar
  • 223
11 votes
2 answers
10k views

I have this while loop and here-document combo which I run in Bash 4.3.48(1) and I don't understand its logic at all. while read file; do source ~/unwe/"$file" done <<-EOF x.sh y.sh EOF ...
Arcticooling's user avatar
  • 4,523
5 votes
2 answers
26k views

When I am shell scripting, the majority of what I am doing is wrapping the I/O of other modules in python, matlab, etc. To do so, I usually use text files or something of that nature with the input/...
Eric's user avatar
  • 153
7 votes
3 answers
6k views

Consider: numbers="1 111 5 23 56 211 63" max=0 for num in ${numbers[@]}; do [ $num -gt $max ]\ && echo "old -> new max = $max -> $num"\ && max=$num ...
tetris11's user avatar
  • 365
3 votes
3 answers
12k views

I'm trying to write a ls wrapper that uses awk to parse the output of ls -lhF. Right now I've split the program into two files - my_ls.sh and my_ls.awk. my_ls.sh's only purpose is to pipe the output ...
westeros91's user avatar
  • 253
5 votes
2 answers
3k views

Standard file descriptors <= 2 are opened by default. A program can write to or read from, a file descriptor after 2, without using the open system call to obtain such a descriptor. The program ...
Mark Galeck's user avatar
  • 223
1 vote
4 answers
5k views

I was hoping to do something like this: echo 'foo' >&3 3| cat Basically, I want to write 'foo' to 3, and then only pipe the data in 3 to cat. But the above doesn't work, I get: bash: 3: Bad ...
Alexander Mills's user avatar
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4 votes
3 answers
4k views

I'm trying to write a bash script that context switches to another user (root, in this case) executes a set of commands to i. create a user (interactively prompting invoker for username) then ii. ...
Nutritioustim's user avatar
  • 255
4 votes
2 answers
5k views

I am writing a bash script to perform some analysis using the program ROOT. I want to run some initial command to load the result of the analysis, then continue using ROOT interactively. The analysis ...
Vesnog's user avatar
  • 689
3 votes
3 answers
2k views

This script was posted as answer to a Question. And I'm trying to work out what's going on. result=$( { { ssh host app-status >&3 3>&-; echo "$?" } | { until read -...
X Tian's user avatar
  • 10.7k
4 votes
1 answer
3k views

There are several questions that use it to do things like multiple output pipes without using process substitution: Is there a way to pipe the output of one program into two other programs? Swapping ...
Sarien's user avatar
  • 143
3 votes
2 answers
2k views

I have managed to create two bash variables, both of which are lines of strings. $oldfilenames which looks like path/old-filename-1.txt path/old-filename-2.txt path/old-filename-3.txt path/old-...
mindlessgreen's user avatar
  • 1,359
3 votes
3 answers
919 views

I want to use a variable from the main shell in a sub shell. I did: export mysql_root_password="test" ( echo $mysql_root_password ) | dialog --gauge "Working hard..." 6 50 There is no output. Of ...
TheNiceGuy's user avatar
  • 915
4 votes
1 answer
1k views

I would like to write a small wrapper around ps so that no matter what the options are or if I grep the result, I could have the first line of the output of ps which tells me what the columns are. ...
hforrat's user avatar
  • 43
3 votes
1 answer
4k views

I am trying to take the input from a serial port and write it to a file and also then read the file and send it back out the serial port to the host computer. A coworker suggested using the "tee" ...
Julien's user avatar
  • 31
1 vote
3 answers
3k views

How do you open a file descriptor and echo it to a terminal while it's being written to from a process? I have a backup program, Duplicity, that writes its logs to a file descriptor specified by the -...
Cerin's user avatar
  • 1,856

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