The shell is unix's command-line interface. You can type commands in a shell interactively, or write scripts to automate tasks.

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6
votes
3answers
1k views

How to defer variable expansion

I was wanting to initialize some strings at the top of my script with variables that have no yet been set, such as: str1='I went to ${PLACE} and saw ${EVENT}' str2='If you do ${ACTION} you will ...
0
votes
1answer
477 views

Converting update-rc.d redis_6379 defaults to chkconfig command

I'm trying to run the commmand below to Centos and of course I get command not found. How do I then convert it to chkconfig ? update-rc.d redis_6379 defaults
1
vote
0answers
353 views

Manually setting environment variables for Metasploit

How do I set manually environment variables for Metasploit, when I execute db_driver I get this message: [*] No Active Driver [*] Available: [*] DB Support: Enable the postgresql driver ...
7
votes
2answers
880 views

How does a shell (bash, for example) expand wildcard patterns?

Assume that a directory has 100 files starting with the letter 'a'. If I do a grep <some string> a* from the terminal, how will the shell handle this? Will it expand the regular expression, ...
21
votes
4answers
40k views

How do I grep for multiple patterns?

I want to find all lines in several files that match one of two patterns. I tried to find the patterns I'm looking for by typing grep (foo|bar) *.txt but the shell interprets the | as a pipe and ...
1
vote
1answer
57 views

Single command to login to SSH and run program?

Is there a way to structure a single command to login via SSH to a remote server and run a program on the remote login shell? In the OpenSSH manual, it reads "If command is specified, it is executed ...
2
votes
2answers
106 views

grep and directories containing spaces

I would like to search all files containing an association of strings (here the files should contain 'arthur' AND ('déni' OR 'deni') for instance) in a directory and subdirectories. After some search ...
3
votes
4answers
186 views

find -exec exit 1 \; Doesn't work neither does find -exec sh -c exit 1 \;

Using Enterprise Linux 5/6, Bash 4.x I want this type of logic: # IF temp file exists, exit because we are restarting already find /tmp/restarting_server -mmin -10 -exec exit 1 lsof -i TCP:1234 ...
7
votes
2answers
603 views

how to output text to both screen and file inside a shell script?

Currently I have a shell script which logs messages to a log file like this: log_file="/some/dir/log_file.log" echo "some text" >> $log_file do_some_command echo "more text" >> $log_file ...
5
votes
1answer
167 views

When is it important to write portable scripts?

Most code I write is in PHP. I have recently started learning shell scripting. Most of the resources and tutorials that I've come across are specific to Bash. Some warn about bashisms and some don't. ...
1
vote
1answer
71 views

How to exit out of the shell script successfully so that python subprocess think it is successfull exit? [closed]

Below is my shell script which simply execute a url like this http://example.com:8080/beat and parse the response and verify certain conditions on it. If that condition is met, then exit successfully ...
1
vote
3answers
43 views

Executing bash shell scripts

I am reading an article on executing bash shell scripts. Method 1: Create a directory for your shell scripts and add the directory to the contents of the PATH variable, so that you can execute the ...
0
votes
1answer
36 views

Updating last modified time of a file

I have created a script to read 15 pcap files from a folder and merge then into one file using mergecap command. I want the merged file to have the creation time same as the first file of the 15 files ...
11
votes
4answers
1k views

Is it possible to configure ctrl-w (delete word)?

Normally, Ctrl-w deletes back to the last whitespace. Is it possible to configure it to use additional characters, such as /? Edit: To be more clear: I don't want to configure the key for it, I want ...
15
votes
2answers
323 views

Quoting within $(command substitution) in Bash

In my Bash environment I use variables containing spaces, and I use these variables within command substitution. Unfortunately I cannot find the answer on SE. What is the correct way to quote my ...
16
votes
2answers
397 views

How can a bash script detect if it is running in the background?

Is there way for a bash script to know if it is running in the foreground or background, and so it can behave slightly differently in each case?
5
votes
2answers
354 views

Making sure a command has executed in bash

I have a bash file with commands to merge pcap files. I want to know if there is anyway to make sure a line in bash runs or not. Like in windows bat file we have %ErrorLevel% ¨ Say a command touch -r ...
-4
votes
3answers
131 views

How to get IP Address using shell script? [duplicate]

Want to get the IP address using Shell script. Without knowing the eth0 or eth1 or eth2 How to get the particular IP address. I am not interest to get localhost address, want to get private IP ...
-4
votes
4answers
86 views

How to add a 3 lines in a file using shell script? [closed]

I have a file, that file contain 10 lines. And now I want to add 3 lines to end of the file using shell script. After add lines, If I run the script again I don't want to add same lines again. ...
3
votes
3answers
47 views

Force shell command to return [closed]

I'm running a command (not part of the standard distro) that sometimes does not return the cursor. That is, I have to press enter myself. The issue is that if I want to do it from a C++ program, ...
1
vote
1answer
26 views

Pass login messages to tmux

When I login, I connect to a tmux session (either by exec'ing tmux if there is no current session, or exec'ing tmux attach if there is). However this means I don't see the login messages (/etc/issue, ...
18
votes
1answer
1k views

Aliases vs functions vs scripts

This site says, "Shell functions are faster [than aliases]. Aliases are looked up after functions and thus resolving is slower. While aliases are easier to understand, shell functions are preferred ...
7
votes
1answer
324 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 < ...
1
vote
1answer
71 views

Command works with tilde at the end. How?

I'm on Ubuntu. I have a script called myscripts in /usr/bin/myscripts This script simply changes the current directory to ~/Work/MyScripts Normally, I simply open a terminal and type ~/Desktop$ . ...
1
vote
0answers
34 views

Logging into multiple SSH servers as root and create an user with same power as root does [closed]

I need a script from which I can log into multiple servers as root (but not all root passwords are same;there are 3-4 different root passwords) and make a superuser (user with same access as root) but ...
4
votes
3answers
86 views

Search for specified keywords in files and copy to a new filename based on the keyword

I'm trying to create an .sh script where if any keyword is found in a file then copy that file to the directory /pathtofolder/keywords/$thefirstkeywordfound (overwrite the file if it already exists). ...
2
votes
2answers
43 views

What does `env COLUMNS=%S ps …` do?

I have seen the syntax env COLUMNS=%sin shell scripts, e.g. see the line below from the Helm package in Emacs: env COLUMNS=%s ps -axo pid,user,pri,nice,ucomm,tty,start,vsz,%%cpu,%%mem,etime,command ...
21
votes
4answers
1k views

Is the shell permitted to optimize out useless terminating commands?

If a shell is asked to perform a probably useless (or partially useless) command known to terminate, such as cat hugeregularfile.txt > /dev/null, can it skip that command's execution (or execute a ...
2
votes
2answers
105 views

Why does bash add single quotes to unquoted failed pathname expansions in a command before executing it?

I was exploring the tracing of commands using set -x (set +x to unset) in bash: Print a trace of simple commands, for commands, case commands, select commands, and arithmetic for commands and ...
2
votes
1answer
88 views

How to find files that contain newline in filename?

I am trying to find files that have a newline in the filename. But I can't figure out what pattern to use. The following works, but is not very useful if I want to use it in indented code. find . ...
1
vote
2answers
77 views

Running a bash script as root prevents asynchronous execution?

The script below get's executed differently if run as a root user. #!/bin/sh gnome-terminal -x sleep 10 echo 'Why must I wait for sleep to finish?' If its run as a regular user, message is ...
2
votes
2answers
43 views

In OS X Darwin, why can I interfere with text input across user sessions using cat?

OS X Darwin: Disrupting Terminal Sessions Across User Identities How, in Brief: with cat < /dev/ttys_, in Terminal. My Question This OS X 10.9.2 Darwin behaviour seems odd to me, and I would ...
5
votes
3answers
1k views

How to wget Youtube horrible URL

I'm going to wget youtube search page where the URL is horrible. This is example when searching searchkeyword sorted by upload date: wget ...
3
votes
3answers
325 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 ...
4
votes
2answers
142 views

Replace string with sequential index

Can someone suggest an elegant way to accomplish this? Input: test instant () test instant () ... test instant () //total 1000 lines output should be: test instant1 () test ...
5
votes
4answers
144 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?
1
vote
1answer
53 views

How do I rename lots of files on a directory without changing their extensions? [duplicate]

I have a problem! I have a bunch of image files with extensions. Jpg and. Png. I wrote a script that renames the files, changing their names in a pattern followed by a number like this: ... ...
2
votes
3answers
93 views

creation of user add

I'm having more then 59 servers I need to create a script for user add. purpose: if I'm creating a user in one server it will be reflected on all 59 servers. How can I accomplish this?
-1
votes
1answer
42 views

Remove directory without `rm -r`

How to remove non-empty directory without using rm -r or find -delete ? I think it is related to unlink, perl or inode
1
vote
2answers
67 views

Free disk space from a JBoss log file which is still being written to

Is there any locking on the content, imposed by the process if at all the process is using the file. We host a JBoss app server on a RHEL 6.4 OS and due to the disk space constraints we have decided ...
0
votes
3answers
64 views

echo bytes to a file

I'm trying to connect my rasberry Pi to some display using the i2c bus. To get started I wanted to manually write stuff, bytes in particular to a file. How do you write specific bytes to a file? I ...
3
votes
1answer
64 views

chmod + silent mode + how force exit code 0 in spite of error

Is it possible execute chmod and ignore error from command Example ( remark file.txt not exsist to show the example ) When I type chmod 777 file.txt I get error on the output chmod: cannot ...
0
votes
1answer
33 views

How to write simple if condition in ash?

I would like to write a small script that would check every once in a while if I have the internet connection. I would like to run it in crontab on my router where I have ash. I am having a hard ...
3
votes
3answers
340 views

if/then/else man page

I would like to know if there is any man page documenting the construction of the most basic script commands like if/then/else, while, for each, and all the relative switches, like -eq, -e, -ge, and ...
1
vote
1answer
290 views

Exit of “> ” mode in Unix shell

In sh (not Bash), how would we abort execution of command when the prompt is in > mode? For example, when entering a string with quotes only at the beginning, it makes the prompt look like >, ...
1
vote
7answers
133 views

what are some uses of .(single period) & ..(double period) in the shell command line

The single period . means current working directory The double period .. means parent of the current working directory I can only think of . being used in relative pathname etc cd ./bin/usr How are ...
8
votes
2answers
238 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 ...
6
votes
7answers
7k views

List only regular files (but not directories) in current directory

I can use ls -ld */ to list all the directory entries in the current directory. Is there a similarly easy way to just list all the regular files in the current directory? I know I can use find find . ...
3
votes
6answers
172 views

Run script in current shell without . before command

If a script should be executed in the current shell, it can be achieved by adding a dot before the command: . ./somescript.sh Is there a way to do this without typing the dot every time? For ...
1
vote
2answers
56 views

Script always runs two instances

I was just curious, what may be the reason why script run two instances when executed. Whenever I run my script foo.sh, and when I check using: $ ps -ef | grep foo.sh It always returns two ...