Chains the standard streams of a series of commands

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15
votes
7answers
5k views

How to pipe output from one process to another but only execute if the first has output?

How can I rewrite this command to only email if there is output from the mailq | grep? mailq | egrep 'rejected|refused' -A 5 -B 5 | mail -s 'dd' email@email Is this even possible on one line?
53
votes
4answers
49k views

How big is the pipe buffer?

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 ...
9
votes
1answer
732 views

I'm confused as to why “| true” in a makefile has the same effect as “|| true”

I have a makefile where I'm stopping a service before removing a file. When it couldn't stop the service, it would break on error. This is clearly unwanted so I thought I'd add || true but missed a |. ...
4
votes
1answer
606 views

Is it possible to send a keyboard event to a background script that's expecting user interaction? (Using 'read')

Ex: $read & [1] 15139 [1]+ Stopped $jobs -l [1]+ 15139 Stopped (tty input) read
14
votes
2answers
2k views

Where do my ANSI escape codes go when I pipe to another process? Can I keep them?

I sometime want to pipe the color-coded output fror a process, eg. grep... but when I pipe it to another process, eg. sed, the color codes are lost... Is the some way to keep thes codes intact ? ...
32
votes
4answers
26k views

What is the mknod command used for?

I just started using Ubuntu as my main OS and I wanted to learn about things I should not do, and learn by the bad things people have done in the past. I came across these email about horror stories ...
4
votes
2answers
838 views

find arcana: can't get pipe to work in -exec line

How do I pipe the results of a find through a sed to xform the stream, and then use that transformed stream as one of two arguments to a script? IE: find turns up file1.tiff (among others) sed ...
21
votes
2answers
10k views

/proc/PID/fd/X link number

In Linux, in /proc/PID/fd/X, the links for file descriptors that are pipes or sockets have a number, like: l-wx------ 1 user user 64 Mar 24 00:05 1 -> pipe:[6839] l-wx------ 1 user user 64 Mar 24 ...
7
votes
2answers
10k views

Why is my variable local one 'while read' loop, but not in another seemingly similar loop? [duplicate]

Why do I get different values for $x from the snippets below? #!/bin/bash x=1 echo fred>junk ; while read var ; do x=55 ; done <junk echo x=$x # x=55 .. I'd expect this result x=1 cat ...
3
votes
1answer
733 views

Can splice()/tee() be made to work with sockets, and not merely pipes?

On Linux, the system calls splice(2) and tee(2) are used to transfer data between two file descriptors. One or both of the file descriptors must be a pipe, according to documentation. Why? Can this be ...
2
votes
2answers
439 views

stop pipe() opening stdin

I've currently got code that forks two processes. The first reads a http streaming radio and pushes the data down a pipe (opened with pipe() ) for the second process to read, decode and output to the ...
36
votes
5answers
10k views

Program that passes STDIN to STDOUT with color codes stripped?

I have a command that produces output in color, and I would like to pipe it into a file with the color codes stripped out. Is there a command that works like cat except that it strips color codes? I ...
4
votes
2answers
1k views

What is the MIME equivalent of uuencode for sendmail?

e.g., I've got files I want to send by sendmail but the receiving mailbox (for posting pictures to my blog) will not accept uuencode files a la $uuencode file | sendmail user@domain I'm guessing ...
6
votes
3answers
321 views

Correct textual name for <<

I've just come across the << command, used like so: cat > outfile.txt <<EOF Multi-line content that will be written to outfile.txt EOF Now, I've no idea what this is called, but I'd ...
5
votes
3answers
706 views

Why does sed act differently depending on the output file?

If I run: cat messages.txt | sed -e 's/a/a/g' > messages.txt on one large file (2500+ lines) I find that the resulting file will only have about 900 lines after the command in cygwin and will ...
0
votes
2answers
2k views

Unix - Filter Commands

I want to know about the "filter-command" which are available in Unix. I am confused regarding this: What is the purpose of "Filter-Command" ? Which are the Filter-commands available in Unix? I ...
7
votes
3answers
6k views

Redirect stdout over ssh

I would like to run something > file on a remote system through ssh, but if I run ssh host something > file the redirection is executed locally as ssh etc > file I've tried it with ' ...
30
votes
4answers
11k views

Can't pipe into diff?

I wanted to be clever and compare a remote file to a local file without downloading it. I can get the contents of the remote file by ssh user@remote-host "cat path/file.name" However, piping that ...
159
votes
10answers
59k views

Turn off buffering in pipe

I have a script which calls two commands: long_running_command | print_progress The long_running_command prints a progress but I'm unhappy with it. I'm using print_progress to make it more nice ...