1
vote
1answer
40 views

Linux : how to redirect stdout & stderr to logger?

I have a program I need to run at startup, it has output on stdout and stderr that I want to redirect to the system log using the logger command. What I have in my startup script is thie: ...
1
vote
2answers
81 views

Linux Shell fundamentals: How can I check the file descriptors status, (where are redirected to) right now without lsof?

I am learning about file descriptors for the case of Linux, and I was wondering if there is any command showing a complete list that allows me to know where is each one redirected to in this moment. ...
8
votes
2answers
113 views

How do I elevate privileges in the middle of pipeline?

My guess was as follows: echo "Generating some text" | su - -c cat >/output/file But su says: su: must be run from a terminal What would you do?
24
votes
4answers
3k views

What is the correct name for the “>” command

I was trying to find how to pass some text to a file without overwriting what's there already using the > command and I realised I don't know what it's called. Searching for right arrow or right ...
4
votes
2answers
65 views

Command substitution vs I/O Redirection?

I am wondered about differences between I/O Redirection and Command substitution? For example when I want to redirect which command output to cd command (I know that it's not a directory) then the ...
2
votes
3answers
81 views

Redirecting only stderr to a pipe

This code snippet is from Advanced Bash Scripting Guide. # Redirecting only stderr to a pipe. exec 3>&1 # Save current "value" of stdout. ls -l 2>&1 ...
1
vote
1answer
53 views

Why does redirection in crontab result in a zero byte file?

System: Xubuntu 13.10 When I have this crontab entry */5 * * * * cat /home/dbk/.bash_aliases &> /home/dbk/Desktop/junk junk has a byte size of 0. Running $ cat /home/dbk/.bash_aliases ...
3
votes
1answer
86 views

What does exec 3<&1 do?

I understand exec can do I/O Redirection on current shell level. but I only sees usage like exec 6<&0 # Link file descriptor #6 with stdin. # Saves stdin. exec 6>&1 # ...
0
votes
2answers
54 views

How to reset the file descriptor

I was trying to use file descriptor for printing the lines in the file #!/usr/bin/ksh exec 3<&0 exec 0< file.txt while read LINE do echo “$LINE” done and I am done with my code ,it ...
7
votes
1answer
323 views

Is this redirecting to /dev/null?

I found this script on the arch wiki which prefixes an ffmpeg command like this < /dev/null ffmpeg -i "$a" -qscale:a 0 "${a[@]/%flac/mp3}" I understand the ffmpeg command, it is the < ...
8
votes
2answers
232 views

Why does 'nohup command >& /dev/null' seem to “work” in some shells?

I edited an answer on Ask Ubuntu that was suggesting the following nohup gedit >& /dev/null & When they actually meant nohup gedit &> /dev/null & Now, the latter ...
0
votes
1answer
28 views

Capture Error of LS to file [duplicate]

#!/bin/sh if [ $(ls sample01.log | wc -l) = 1 ] then echo "File Found" > lsOutput.log else echo "File Not Found" > lsOutput.log fi But if sample01.log is not already existing my code already ...
4
votes
1answer
134 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 ...
2
votes
1answer
58 views

< and << in UNIX /Linux

What is the option <<and < are used in linux for??? For example cat << abc.txt I know its a stupid question, but i was not able to search it on google as i did not know what ...
4
votes
1answer
72 views

Can redirecting stdout and stderr to the same file mangle lines?

I've read that when redirecting stdout and stderr to the same file using 2>&1, stdout is usually block buffered while stderr is unbuffered. If a very long line is written to stdout, requiring ...
4
votes
3answers
201 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 ...
3
votes
2answers
107 views

Save find -exec output to text file

I have a set of videos in the folder. I would like to get the info about this videos using ffmpeg -i command and save the output to file. So I wrote the line: find . -type f -exec ffmpeg -i {} \; ...
0
votes
4answers
131 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 ...
1
vote
1answer
50 views

Alias for redirecting both standard output and standard error, as well as sending to background [duplicate]

I am trying to create an alias for redirecting both standard output and standard error of gedit to /dev/null, whilst sending the command to background. This works: $ alias gedit='gedit $1 > ...
2
votes
2answers
72 views

Error message on terminal despite using 2> symbol

Why does this command show error message despite using 2> symbol? cat < foo 2>bar bash : cannot open foo : No such file or directory
1
vote
1answer
55 views

Crontab Triple Redirect

I have a very basic understanding of redirects, but I have come across a cronjob with redirects which I do not understand. 00 19 * * 1-5 /apps/app/scripts/doit.sh a np cron > ...
4
votes
3answers
235 views

How do you process an entire command as sudo that involves redirecting or piping?

I am trying to follow what I assume is best practises of using sudo instead of root account. I am running a simple concat file operation such as: sudo echo 'clock_hctosys="YES"' >> ...
3
votes
3answers
60 views

capture output from command without interference

How can I test whether a command's output is an empty string without interfering with said output? Example: command | ??? if [ $? = 0 ] && [ -n "$output_from_command"]; then ... I'd ...
8
votes
3answers
325 views

Why does the less-than sign not work as a replacement for cat in bash?

I heard about "useless use of cat" and found some suggestions, but the following outputs nothing in my bash shell. < filename Using cat works as expected though. cat filename I'm using Fedora ...
12
votes
2answers
154 views

Output order with process substitution

This is what I usually do to run grep and wc on a file without having to scan it twice <file.txt tee >(grep LITERAL) >(wc -l) >/dev/null However, this yields EXEC LITERAL 32 ...
0
votes
1answer
51 views

&> redirection not working correctly

Please see the following shell transcript: $ ls input.txt test-amp-gt.sh test-both-2.sh test-both.sh test-gt.sh $ cat input.txt input file $ cat test-gt.sh #! /bin/sh cat input.txt > ...
2
votes
1answer
111 views

What does the expression $(<“dir/file”) mean in bash?

In a bash script I cannot post here I see the following expression: $(<"dir/file") From what I understand the expression $(...) evaluates a command inside (as when using backticks), but what is ...
10
votes
3answers
183 views

How to “combine” lines printed by multiple programs safely?

Suppose I want to execute multiple programs in parallel and combine their outputs to one pipe: sh -c ' (echo qqq; echo qqq2; echo qqq3)& (echo www; echo www2; echo www3)& (echo ...
7
votes
3answers
220 views

Redirect output from all commands to file, not just last

I want to add a header to a file with echo, then use a command to create the rest of the file. This means I'll be using two separate commands. How do I write the output from both commands to a file ...
2
votes
2answers
134 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 ...
15
votes
2answers
454 views

How can I stream data to a program that expects to read data from a file that is given as a argument?

I have a huge gzipped file and I want a program (4s-import in this case) to read it. It takes a lot of time to first unzip the file and then call the program with the path to the file as an argument. ...
12
votes
2answers
326 views

Redirecting using >|

Can someone explain the utility of using >| for redirecting output to a file instead of just >? When I was shown this technique the explanation was that this guaranteed the file was truncated ...
2
votes
2answers
187 views

What is the use of “&>>” in bash?

I was studying a bash script code where I encountered operator "&>>". I didn't understand its use. So, I referred to http://www.gnu.org/software/bash/manual/html_node/Redirections.html . It is ...
2
votes
1answer
40 views

Inner logic of chained redirections

When I type cat some_file > new_file1 > new_file2 I got output from some_file in new_file2 and empty new_file1. What is the inner logic in it? More specifically what is the stdout of file? ...
3
votes
2answers
337 views

Who is file owner if the file is created using sudo command?

I logged in using my username ravbholua: ravbholua@ravbholua-Aspire-5315:~$ echo $LOGNAME ravbholua I create file named a1: ravbholua@ravbholua-Aspire-5315:~$ echo>a1 ...
5
votes
1answer
86 views

Replacing stdout with stderr

Is it possible to redirect the output from a command to replace the text sent to stdout with the text from stderr? $ ./script this line is redirected to stdout this line is redirected to stderr $ ...
3
votes
2answers
341 views

What does “sh a.sh <&0 >&0” mean?

It's a question about bash shell command. "sh a.sh <&0 >&0" What dose it mean? Especially, I'm not very clear about what does &0 mean?
2
votes
1answer
102 views

xargs and < and > to the same files

I want to run git stripspace on all my source code files, on each build (or precommit or just manually), to remove extraneous whitespace, and later maybe to format the code in a standard way, So ...
9
votes
3answers
249 views

Is this a typo in Bash manual's redirection section?

Note that the order of redirections is significant. For example, the command ls > dirlist 2>&1 directs both standard output and standard error to the file dirlist, while ...
2
votes
2answers
105 views

Is it possible to create a “file” that can be used by any process without actually saving the file on disk?

Suppose I do a grep that gives me a lot of results. I want to use the output of grep and pass it to a command that takes a filename as it's first argument. For example - myCommand filename.txt I ...
2
votes
3answers
667 views

How to stop redirection in bash

I use : exec >script.log 2>&1 in my script to redirect all output to a file. At the end of the script I would like to print a message to the screen. How do I stop the redirection?
0
votes
1answer
992 views

Redirect both stderr and stdout to /dev/null with /bin/sh

Tried all sorts of ways to redirect both stdout and stderr to /dev/null without any success. I have almost my entire life run bash which i've never had this issue with but for once in BSD i'm stuck ...
3
votes
2answers
120 views

Do redirection operators always open file descriptors in parallel?

1. Consider snippet#1: $ cat test.txt > test.txt cat: test.txt: input file is output file It seems that cat makes its input file descriptor point to test.txt and then when it tries to set its ...
2
votes
3answers
231 views

How to use arguments with 'find -exec'? [duplicate]

I'm trying to generate static html files for all php scripts inside dir: find . -name "*.php" -exec php {} > {}.html \; But it just dumps all results to {}.html. How to do it properly? And how ...
3
votes
3answers
324 views

Concatenating thousands of files: > vs >>

I found two seemingly contradictory answers on StackOverflow to the following questions: Concatenating Thousands of Text Files Across Hundreds of Directories (while keeping some structure) How do I ...
26
votes
2answers
1k views

Command line: <<< instead of <<

Why is the command md5sum <<< 'ddd' (output: d6d88f2e50080b9602da53dac1102762 -) right, and md5sum << 'ddd' not? What does <<< mean?
2
votes
1answer
1k views

redirection to file issues with nohup and pipe

For the following command: ssh -t esolve@hostname 'sudo nohup bash -c "ls > log 2>&1 &"' I always got error information: nohup: ignoring input and appending output to ...
1
vote
1answer
101 views

Standard I/O File Descriptors

I am new to Shell SCripting I code this $ ls -l 1> stdout.txt and I get the output as desired, 1> stdout.txt redirects the output from standard output to the file stdout.txt. I don't ...
4
votes
4answers
517 views

Getting stdin from a named pipe

What I am trying to do is run python in a terminal window and redirect it's stdin from a named pipe. Then I write to the named pipe in another terminal and have that command execute on python. ...
1
vote
2answers
131 views

Nested read fails

I have a list of filenames in a file and want to do let the user decide what to do with each. In bash, iterating over filenames is not trivial in itself, so I followed this answer: #!/bin/bash while ...