Chains the standard streams of a series of commands

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1
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1answer
59 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
322 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 ...
3
votes
5answers
10k 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 ...
2
votes
2answers
246 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
554 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
282 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
68 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
357 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 ...
4
votes
2answers
3k 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
219 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 ...
17
votes
9answers
2k 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
120 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
854 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
503 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
113 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. ...
4
votes
3answers
258 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
102 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
616 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
752 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
192 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 ...
9
votes
4answers
5k 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?
2
votes
3answers
348 views

How can I tell echo/printf in Bash to swallow escape codes, based on a condition?

I have a Bash script that is being run interactively and as a cron job. When run interactively it outputs colored text on the terminal. However, when run in cron it doesn't have a terminal and ...
3
votes
4answers
161 views

saving output of another command

I need to select certain lines from the log file and also save them to a text file. I tried the following but none of them are working as expected. The file "todel.txt" shows 0 bytes. tail -f ...
2
votes
2answers
412 views

Pipe command to tail: when is the first command aborted?

In this example: $ for i in {1..3}; do sleep 1; echo $i; done | head -n 2 why is the first command (for loop) killed only just before the 3 is displayed ? I expected it to be killed right after ...
2
votes
1answer
357 views

Appending to same array in various loops, only last values remain Bash 4

I have something like this: FILES=() for i in *.map do FILES+=($i) done find /var/candy -name "chocolate_[0-9]" | while read snack do FILES+=($snack) done for file in ...
1
vote
1answer
160 views

`cat /dev/ttyACM` loses data when piped through netcat

I'm reading data from /dev/ttyACM0 using cat /dev/ttyACM0 on a Raspberry Pi. The data comes from a device, which sends lines in the form 15.00 1316013 15 where the first number is a value, the ...
2
votes
1answer
866 views

Linux nuisance: /dev/stdin doesn't work with sockets

Linux has this blitheringly annoying peculiarity that /dev/stdin won't work with sockets - it is hardcoded to return ENXIO. Try this: socat TCP-OPEN:localhost:1234 EXEC:cat\ /dev/stdin,nofork ...
2
votes
1answer
447 views

Piping Sox and FFMPEG together

I'm processing a variety of audio files in a bunch of different formats and I'd like to unify their format and configuration using FFMPEG and SoX. There are two steps to my process: Convert the ...
22
votes
5answers
2k views

Pipe to multiple files in the shell

I have an application which will produce a large amount of data which I do not wish to store onto the disk. The application mostly outputs data which I do not wish to use, but a set of useful ...
1
vote
1answer
214 views

Pipe input to another process one line at a time

I have a script which can take one file name at a time and I want to run it for many files in a folder. So, I want to pipe the output of: find . -iname '*.m' to my script but one line at a time. ...
2
votes
3answers
726 views

Running tcpdump, tee and scp

I'm trying to run the following: $ tcpdump -l -X -i eth1 -n tcp port <port> | tee capture.txt | \ scp capture.txt root@10.3.3.227:/home/checker/ tcpdump -l -X -i eth1 -n tcp port ...
13
votes
4answers
283 views

pipe, { list; } only works with some programs

Need explanations from power users for such unpredictable behaviour: ps -eF | { head -n 1;grep worker; } UID PID PPID C SZ RSS PSR STIME TTY TIME CMD root 441 2 0 ...
0
votes
1answer
380 views

What is the meaning of cut's -d and -f options

How can this pipeline be explained: cat /etc/passwd | cut -d : -f 9 2>&1 | sort | uniq 2>&1 | wc -l I'm learning Unix by myself and I don't really get it. What does cut -d : -f 7 ...
5
votes
2answers
321 views

Is there a line-by-line bash pipe?

I remember reading somewhere (then I forgot where) about a rarely used type of bash pipe that could redirect output line-by-line. In other words, rather than redirecting the output once at the end, ...
12
votes
3answers
446 views

How to display the number of lines output by a command in real time?

I'm using svn export as part of a packager script for my application, and it looks like this command, like many others, doesn't have any kind of progress bar. I have two choices at the moment: ...
1
vote
1answer
134 views

Piped Logs in Apache?

Can someone walk me though how the data flows? Need to understand how I can intercept the log data, make changes to that data in situ, then save to a file.
5
votes
3answers
957 views

Why can't certain programs (like readlink) take input from a pipe?

I have a symbolic link to a script in my $PATH whose file I wanted to edit. I forgot the filepath, so I tried to do the following: $ which my_script_link | readlink I expected that to output the ...
1
vote
1answer
132 views

Pipe not picking up stdout

I am running a java program from a OS X 10.8 bash terminal, and are trying to rederect the output it is producing. However, when either running this throug a pipe, or rederecting it to a file, the ...
4
votes
3answers
634 views

Split stdin by lines

I want to invoke a command for every line of the standard input, much like xargs, but the line should be passed as standard input, not as a command-line argument: cat some-file.txt | <magic> | ...
6
votes
5answers
391 views

Is it possible to feed Open Office via STDIN?

I have an Open Office Spreadsheet document stored inside a bash variable. I want to do something like the following to feed Open Office via STDIN: echo "$openOfficeDoc" | ooffice But it doesn't ...
1
vote
1answer
182 views

Flush data to file frequently for long running command? [duplicate]

I have a command that processes data slowly. The command processes lines from a file and writes the results to the output file data.txt: my_command > data.txt The issue I have is that I'd like to ...
1
vote
2answers
237 views

How to tell the “last” command to read from STDIN?

SERVER:~ # zcat /var/log/wtmp-20130827.gz | last -f - last: -: No such file or directory SERVER:~ # Without uncompressing the wtmp file, how can I see the output of if it with the last command?
7
votes
2answers
316 views

Use keyboard-interactive authentication when piping ssh output to other command

I'd like to pipe the output of ssh to a different command. For example: ssh myserver cat remote-file | diff local-file - The problem is that myserver asks for a password, but I can't enter it. (For ...
4
votes
1answer
1k views

find and rysnc?

I want to be able to search for files over 14 days and over 10k and than rsync those found files to a destination. Is there a way to combine these two commands? find ./ -mtime +14 -size +10k rsync ...
2
votes
1answer
70 views

Pipeline each line of a file to a specific variable in a second command

I want to execute the following instruction: basex -bword=ENTRY consulta.xq But for every line of a SampleText file (plain text mainly). The SampleText contains the following lines: hello evening ...
5
votes
1answer
2k views

Piping search term (not filename) to grep

I want to pick out certain lines containing a given number from a file. The file I want to search is called os_clusters/piRNA_clusters.bed. awk '{if (a[$0]++ == 0) {split($0,b,"."); ...
5
votes
3answers
316 views

Can you pipe to a .bash_profile function?

I received a great function for highlighting files in Apple's finder using the command-line. It's basically a wrapper for osascript. I got it from Mac OS X: How to change the color label of files ...
6
votes
2answers
2k views

How to download an archive and extract it without saving the archive to disk?

I'd like to download, and extract an archive under a given directory. Here is how I've been doing it so far: wget http://downloads.mysql.com/source/dbt2-0.37.50.3.tar.gz tar zxf dbt2-0.37.50.3.tar.gz ...
2
votes
3answers
127 views

Expand placeholders with same-named environment vars in text file?

There are a lot of variations on this question, but I wanted to ask it here anyways because I am so close (!) to finding a solution on this one - I just need a little nudge. Scenario I have several ...
3
votes
3answers
12k views

What makes a Unix process die with Broken pipe?

Here are some options I thought of, not sure which is the right one. a) There was an I/O error reading from the pipe. b) The process writing to the other end of the pipe died with a failure. c) All ...