Login or Register to Ask a Question and Join Our Community

Sponsored Content
Full Discussion: Question on bash redirection
Top Forums UNIX for Beginners Questions & Answers Question on bash redirection Post 303035997 by MadeInGermany on Wednesday 12th of June 2019 01:51:45 AM
Old 06-12-2019
x < y means: run command x and feed its input (stdin) from file y.
It is true that file y is opened for reading before command x runs.
diff <(sort testfile.txt) <(sort testfile2.txt) means: open a device ("/dev/fd/..."), run sort and redirect its output to the device, open another device, run another sort and redirect its output, run diff with the two devices as arguments (that diff treats as input filenames).
Quote:
man bash
...
Process substitution
...
The process list is run asynchronously, and its input or output appears as a filename. This filename is passed as an argument to the current command as the result of the expansion. If the >(list) form is used, writing to the file will provide input for list. If the <(list) form is used, the file passed as an argument should be read to obtain the output of list. Note that no space may appear between the < or > and the left parenthesis, otherwise the construct would be interpreted as a redirection. Process substitution is supported on systems that support named pipes (FIFOs) or the /dev/fd method of naming open files.
...
This User Gave Thanks to MadeInGermany For This Post:
sand1234
 

10 More Discussions You Might Find Interesting

1. Shell Programming and Scripting

Bash multiple output redirection

Hello all. Is there a way to redirect output to more than one file at a time? I have a method1() that writes to a logfile. In the method cksums are done on files by doing a "for i in `ls`; do cksum $i > $LOGFILE done " In the logfile I want to show the cksums under each directory like... (2 Replies)
Discussion started by: yoi2hot4ya
2 Replies

2. Shell Programming and Scripting

question on redirection (<<)

I came across the following problem, where file contents are overwritten using redirection. Can somebody please explain what cat << BAR seems to be doing and say why this is a problem? Explain the contents and relation between the two filenames used before the cat command. thanks /tmp# echo... (2 Replies)
Discussion started by: newkidintown
2 Replies

3. Shell Programming and Scripting

input redirection question

Hi, in my script I need to execute the following command: query $id 456 432 but it waits for a RETURN character from keyboard and therefore, it fails. I tried something like: query $id 456 432 << '\n' but, i'ts clear it is not correct. Is there any way to do this? Thxs. (0 Replies)
Discussion started by: luistid
0 Replies

4. Shell Programming and Scripting

File redirection question

Hi all, I am working with the Grinder tool (unrelated to my question) to redirect the output of a program to a file as follows: java -cp $CLASSPATH net.grinder.TCPProxy > grinder.txt This is a proxy server which pipes output to a file. When I do something on my proxy, more and more goes to... (1 Reply)
Discussion started by: Annorax
1 Replies

5. Shell Programming and Scripting

BASH Problem / Question regarding redirection

Hi all, Maybe someone is able to help: Need to redirect the output of a command in realtime to a second command. Command-A executes a remote shell to another host, and outputs its results. Command-B displays a "dialog" with the outputs of Command-A. Command-A Output: Updating FileA... (2 Replies)
Discussion started by: mharald
2 Replies

6. Shell Programming and Scripting

Redirection Question

I just wondered if I'm understanding this command line correctly cat 2>save1 0<memo | sort 2>save2 1>letter This means that stdin will read from memo and if there is an error then stderr will write to save1. Am I correct in saying that the sort command will sort the memo file and write... (2 Replies)
Discussion started by: snag49ers
2 Replies

7. Shell Programming and Scripting

Question about IO redirection

for shell operators like <, >, <<, and >> do the LHS always have to be a process or device and the RHS a file or device? Is it possible for the RHS to be a process? (1 Reply)
Discussion started by: stevenswj
1 Replies

8. Shell Programming and Scripting

Redirection question

I want to redirect stderr and have the following peice of code $ cat t1.ksh #!/bin/ksh func2() { diff /tmp/jdlkwjdlkejew /tmp/djlkwejdlewdjew >$OUTPUT_FILE 2>>$ERR_FILE } func1() { let counter=0 while do print -u2 "Error: In main function" func2 let... (1 Reply)
Discussion started by: BeefStu
1 Replies

9. Shell Programming and Scripting

Error redirection question

Hi gurus, I have a question, need some of your inputs... I have a command like this : export LINE_COUNT=`wc -l test.dat | awk '{print $1}'` echo $LINE_COUNT --- > gives me 2 which is fine as the file has 2 lines. This works fine if the file test.dat is present but in case... (3 Replies)
Discussion started by: calredd
3 Replies

10. Shell Programming and Scripting

Input redirection within bash script

Hi, when I try to redirect input and the command is described as a string within an array redirection does not work. why? #!/bin/bash dir=("tail < ./hello.txt") tail < ./hello.txt #works ${dir} #does not work (2 Replies)
Discussion started by: heinzel
2 Replies

LEARN ABOUT DEBIAN

smd-server

smd-server(1)						 Sync Mail Dir (smd) documentation					     smd-server(1)

NAME

       smd-server - sends diffs and mails to smd-client

SYNOPSIS

       smd-server [--exclude glob] [-v|--verbose] [-d|--dry-run]
	     [--get-mddiff-cmdline] [--stop-after-diff]
	     [--override-db dbf] [--dump-stdin tgt] endpoint mailboxes

DESCRIPTION

       smd-server needs to know a name (endpoint) for the client (that must not be used by others) and a list of mailboxes (directories).

       smd-server first calls mddiff(1), then prints on stdout the generated diff. It then accepts from stdin a small set of commands a client may
       issue to request a file (or parts of it, like the header).

       smd-server is in charge of committing the db file used by mddiff(1) in case the client communicates a successful sync.

OPTIONS

       -v --verbose
	      Increase program verbosity (printed on stderr)

       -d --dry-run
	      Do not perform any action for real

       -n --no-delete
	      Do not track deleted files

       --exclude glob
	      Exclude paths matching glob

       --override-db dbf
	      Use dbf as the db-file

       --get-mddiff-cmdline
	      Print the command line used for mddiff and then exist

       --stop-after-diff
	      Send the actions to the other endpoint and exit. If used in conjunction with --override-db, dbf is removed just before exiting

       --dump-stdin tgt
	      Dump standard input to tgt and exit

NOTES

       smd-server is a low level utility. You should use higher level tools like smd-pull(1) and smd-push(1)

SEE ALSO

       mddiff(1), smd-client(1), smd-pull(1), smd-push(1)

AUTHOR

       Enrico Tassi <gares@fettunta.org>

								   11 June 2012 						     smd-server(1)
All times are GMT -4. The time now is 05:39 AM.
Unix & Linux Forums Content Copyright 1993-2022. All Rights Reserved.
Privacy Policy