Chains the standard streams of a series of commands

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1answer
61 views

Pipe chain with devices

As far as I know, you can have the ability to make pipes between applications, such as this one: $ step1 < input_file | step2 | step3 > result_file And you can access devices such as ...
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2answers
197 views

bash function output to pipe [closed]

I made a bash function to beautify svn output, this function show logs one line per commit, it is great! I like it, but if I use it with pipe it does not work. You can find it on github svn-beautify ...
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votes
3answers
692 views

How to read user input in pipe?

Let's assume I have a file named confirmation.sh with the following content: #!/bin/bash echo -n "Are you sure [Y/n]? " read line case "$line" in n|N) echo "smth" ;; y|Y) echo "smth" ...
2
votes
2answers
292 views

filter and count with grep in a single pass?

I am using grep at the end of a set of piped commands to filter some rows out of a file. Afterwards I will want to do some arithmetic based on the number of remaining rows. e.g. ...
6
votes
1answer
508 views

bash scripting - read tarball from stdin

I have a task I need to script that I feel should be stupidly simple, but I'm actually having a rather tough time. I have a short bash script that takes a specific type of application in tarball form ...
5
votes
1answer
542 views

Loop through binary data chunks from stdin in Bash

I'm looking for something like while IFS= read -r -n $length str; do ... done but for binary data. Is it possible to do this using dd or other tools? Is there some technique to make these tools able ...
7
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5answers
222 views

Can a program next in a pipeline see the exit code of the previous program?

I would like to make a pipeline of Bash scripts like this prog1 | prog2 such that prog2 can see the exit code of prog1 and act differently based on that information. Is this possible?
4
votes
5answers
461 views

Semi-asynchronous pipe

Assume I have the following pipe: a | b | c | d How to wait for completion of c (or b) in sh or bash? This means that script d can start any time (and does not need to be waited for) but requires ...
4
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1answer
249 views

Why do piping and redirection work differently with here documents?

Combining a redirect with a here document seems logical enough: $ bash > foo <<EOF echo Hello EOF $ less foo Hello But with a pipe it behaves differently: $ bash | tee foo <<EOF ...
3
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2answers
129 views

Pipe / direct image / video output to foreign server

I am working on a Project that involves taking the output from a Webcam which is in either jpg or h.264 format, and outputting it to a foreign server (HTTP / FTP would work, I am open minded). What is ...
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votes
2answers
803 views

How can I redirect `time` output and command output to the same pipe?

Suppose I have a binary called foo. If I want to redirect the output of foo to some other process bar, I could write ./foo | bar. On the other hand, if I wanted to time foo, and redirect the output ...
0
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1answer
51 views

Piped search queries in vim or less

I would like to be able to search a log file for lines that being with ^2014-02-18 15:30:[0-9:,]* and have UserName:someguy much later in the same line. I am sure I could do a regex to include any ...
3
votes
5answers
823 views

Counting files in folder without wc

Why does the following scripts give a count of 0 instead of giving the count of files present in the directory? #!/bin/bash cd /root/Jamshed/script count=0 ls -lrt > all_files cat all_files | ...
2
votes
1answer
752 views

How can I pipe commands to any terminal?

I often use more than one terminal (or terminal emulator) at a time; and while in X I can copy-paste commands, besides not being very practical, it obviously does not work on the real TTY. The first ...
4
votes
2answers
2k views

How to compose bash functions using pipes?

I have few functions defined in this fashion: function f { read and process $1 ... echo $result } I want to compose them together so that invocation would look like f | g | h. What idiom ...
1
vote
3answers
171 views

How to use the pipe command to open a directory after find?

Is there a way to opend found directories (via find) all in one command? One of the things I tried to study several times and never been able to really get, is the effective use of pipe: is it maybe ...
4
votes
3answers
761 views

Please help explain this bash output redirection

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 ...
6
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3answers
723 views

How to modify output in bash command pipeline

For example, I got from some command some lines $ some-command John Bob Lucy Now I'd like to add chaining command, that modifies output. $ some-command | other-command Hi John Bye Hi Bob Bye Hi ...
3
votes
2answers
113 views

Repeated commands in a bash pipeline

Sometimes commands repeat in pipeline command. For example (just to illustrate): $ grep -lF 'pattern' ./foo/**/*.bar | xargs dirname | xargs dirname Is there a way to shorten chaining command? For ...
3
votes
4answers
2k views

Pipe all input and output of terminal to file

I do not know if this is even possible or not, but in an attempt to keep track of many changes I am about to make to my system I want to track all input I type and all output from a terminal I'm ...
1
vote
2answers
845 views

Why does this ssh command not work? (cat ./file | ssh <user@host> “cat | sudo -t -t 'cat > /root/location/file'”)

I'm trying to do the following but it's not quite right. cat ~/Desktop/blah.png | ssh -t -t trusktr@50.116.4.56 "cat | sudo -i 'cat | /path/to/blah.png'" I have my public ssh key in the ...
3
votes
1answer
88 views

How can the order of execution in the shell as it relates to redirection be upset about 1 time out of a 1000 on my system? [duplicate]

Considering this Q&A about the order of execution in the shell as it relates to redirection, and despite the fact that if a file doesn't exist it gets created first so that cat example.txt | shuf ...
0
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4answers
490 views

Why does the command shuf file > file leave an empty file?

I know this is sort of a duplicate of another question (Why this sort command gives me an empty file?) but I wanted to expand on the question in response to the answers given. The command shuf ...
0
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2answers
45 views

How can I use tee to print the input stream?

I have a pipe line that looks like this: cat myfile | awk '$3 > 0 { print $1, $2 * $3 }' | tee >(printf) | perl myscript.pl I would like to print the input to my Perl script using tee. How ...
5
votes
1answer
89 views

Shell one-liner for adding a line in the middle of a pipe

I write a script which sends the input file to CPP, then to grep, then to a certain program: cpp $1 | grep -v "#" | theprogram But, "theprogram" requires the input to start with a certain constant ...
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0answers
95 views

Postfix mail how to debug transmission to mail handling agent

I have a postfix server running on Ubuntu (and Debian previously). The server is configured to read users and groups from an OpenLDAP server and delivers mail first the spam filter and then to a ...
3
votes
2answers
671 views

grep string from contents of file command then delete file

I have a peculiar problem I need help with. I have a large batch of .docx files where a certain number of them are junk. I know how to identify these files from the file command, as they contain the ...
2
votes
1answer
208 views

Piping periodic data between Python scripts

How to receive data from the environment e.g. bash I am trying to launch two Python scripts in bash and pipe stdout from one of them to stdin of the other. The first script outputs a single ...
3
votes
3answers
201 views

Preserving color output with cut

Using bash interactively I am trying to use cut to prevent the lines from going longer than my terminal width. But when using a command with colorized output all the color gets removed by cut. For ...
1
vote
1answer
56 views

Memory-efficient utility to return N first sorted values

I would like to implement a very popular MapReduce example using only existing programs operating in a UNIX way. The problem is to find N most frequent values in an enormous amount of data. The ...
3
votes
1answer
280 views

Why does grep change the length of output lines?

I often use dpkg or aptitude combined with grep when I want to list certain packages available or installed on my system, but I noticed that when I add | grep, the output lines look a little bit ...
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5answers
7k views

Pass the output of previous command to next as an argument

I've a command that outputs data to stdout (command1 -p=aaa -v=bbb -i=4). The output line can have the following value: rate (10%) - name: value - 10Kbps I want to grep that output in order to ...
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votes
2answers
155 views

Piping to the command substitution of a string containing pipes

This works— $ x='grep a' $ echo ab | $x ab This doesn't— $ x='grep a | grep b' $ echo ab | $x grep: |: No such file or directory grep: grep: No such file or directory grep: b: No such file or ...
1
vote
2answers
475 views

Help me understand this echo/spawn/send/expect construct

Here is a line from a bash script I am trying to understand: echo "spawn myscript.sh arg1 arg2; expect \"Please enter your value: \"; send \"myval\r\"; expect eof" | expect I think I understand the ...
4
votes
3answers
201 views

processing command output line by line, without mixing standard input

So, I have a problem very similar to Bash: How to read one line at a time from output of a command?, I am doing: while read path; do mplayer $path; done < <(find-me-random-mp3s) or ...
1
vote
1answer
59 views

Mysql import the most recent file from a directory

I have a directory with daily backups of my entire MySQL database. I want to import the most recent backup into the database. I know to import a backup I need to use mysql -u root -ppasswordhere ...
3
votes
1answer
301 views

How does the piping in this command ultimately achieve to kill the process?

I have seen the following line in a bash script for killing a process(in this case started with the command loadgen): ps xww | grep -i "loadgen" | grep "PATTERNMATCH_FACT.xml" | cut -c1-5 | xargs -i ...
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votes
2answers
2k views

Is there any way to use xargs across a pipe?

I'm trying to automatically convert flac files moved to a folder into mp3 in another folder. My current line of code is this: inotifywait -m -r -q -e moved_to --format "'%w%f'" ~/test | xargs -I x ...
5
votes
1answer
192 views

Replace CD number in MP3 ID3 tag

I have a library of MP3 files where in some files the "CD number" tag (TPOS) contains "CDx" values, e.g. "CD1" or "CD2". The ID3 spec says that TPOS values shall be numerical strings. Processing these ...
16
votes
9answers
1k views

Grep lines but let the first line through [duplicate]

Consider the following output from df. Filesystem Size Used Avail Use% Mounted on /dev/sda1 23G 6.1G 16G 29% / udev 10M 0 10M 0% /dev tmpfs 397M 420K ...
2
votes
3answers
113 views

The processing order and printing of files with find

This simple BASH script collects msgstrs in a PHP project: #!/bin/sh TARGET=/path/to/project LPATH=locale/cy_GB/LC_MESSAGES POFILE=messages.po mkdir -p $LPATH touch $TARGET/$LPATH/$POFILE cd $TARGET ...
24
votes
3answers
680 views

Multicolored Grep

I'm trying to get each grep command to highlight it's results in a different color. I can do it manually with a line like this: ls -l GREP_COLORS='mt=01;32' grep c | GREP_COLORS='mt=01;31' grep o | ...
15
votes
2answers
478 views

Use of ^ as a shell metacharacter

I wrote a small script today which contained grep -q ^local0 /etc/syslog.conf During review, a coworker suggested that ^local0 be quoted because ^ means "pipe" in the Bourne shell. Surprised by ...
3
votes
3answers
102 views

Print a message from the left-hand side of a pipe

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. ...
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votes
3answers
217 views

cycle through one command's output and use in another command [duplicate]

How can I use the output of one command - line-by-line - into another command? I know how to do this with the | pipe symbol, but this uses the entire output in one command. I would like to go line by ...
1
vote
3answers
101 views

Automating pipes?

I find myself using basically the same line over and over again: cat file | command1 | command2 | command3 > file Is there a way I can put all these pipes into one script, so I can just run ...
6
votes
2answers
460 views

Piping data to a process's stdin without causing EOF afterward

I have an executable that starts a user-interactive shell. I would like to, upon launch of the shell, inject a few commands first, then allow the user to have their interactive session. I can do this ...
5
votes
2answers
656 views

Obtaining PID of command earlier in Pipeline

I'm writing a bash script to use inotifywait to monitor a directory and kick off actions when changes are detected. Something like: inotifywait -m ... | while read f; do something; done Since ...
2
votes
2answers
179 views

turn off buffering for `hping` in OpenBSD

It would appear that the output from hping is fully buffered when piped to perl for further line-by-line processing, so piping hping to perl doesn't work. hping --icmp-ts example.ca | perl -ne 'if ...
6
votes
4answers
3k views

how do I trim each line in bash?

I would like to remove all leading and trailing spaces and tabs from each line in an output. Is there a simple tool like trim I could pipe my output into?