Questions about shell scripts, executable files that are interpreted by a shell (bash, zsh, etc.).

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1
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1answer
162 views

What is the difference between ' and "? [duplicate]

I tried to create a text file in a bash script. The echo command spans multiple lines and has some double quotes "". #!/bin/bash echo "blabla bla bla bla "blabla" bla bla " bla bla bla" and so on ...
4
votes
2answers
395 views

Bash-script. Shift seconds

Maybe somebody can help me. In bash I don't know how to do that. I need to do a bash-script. At stdin I have .srt file of subtitles in this format: num HH:MM:SS,SSS --> HH:MM:SS,SSS text line 1 ...
6
votes
2answers
2k views

Detect if running in a virtual terminal?

I'd like to autologin to tty1 on login and then use vlock to lock it. How can I detect from Bash if the current terminal is a console virtual terminal (e.g. tty1), so that I can put the vlock line ...
2
votes
2answers
527 views

mv complains about standard input in a pipeline that filters file name with grep

I'm trying to move several .avi files that have spaces in from a CD to my home folder. I've already know how to get rid of the spaces: find /media/mathscd/ | grep -L -r "*.avi" | for file in *; do ...
3
votes
3answers
773 views

copying specific files in directory

I am trying to copy some of the files in a directory. The directory contains following files my current directory is ~/certificate/ drwxrwxr-x 2 ubuntu ubuntu 4096 Oct 16 11:58 apache -rw-rw-r-- ...
4
votes
1answer
318 views

returncode of command in a pipline [duplicate]

The following script runs on Solaris using /bin/ksh and on Linux using /bin/sh cmd | tee -a cmd.log | tail exit $? The output of cmd is saved in a file cmd.log and the last lines are displayed on ...
1
vote
1answer
399 views

Binary search for a failing line

git has bisect run to figure out which revision an error was introduced. I have a big file (100GB) and at least one of the lines is bad, but the program I have to check it with will not tell me which ...
2
votes
3answers
175 views

How can i get five seconds of data appended to the end of file?

suppose if a shell script appends a data to a file.txt like 1........... 2........... 3............. 4............. 5.............. Now i want another script that could check the fresh data ...
23
votes
6answers
57k views

Delete First line of a file

How can I delete the first line of a file and keep the changes? I tried this but it erases the whole content of the file. $sed 1d file.txt > file.txt
3
votes
1answer
109 views

Shell Script Size 57M

I have recently Downloaded yEd Graph Editor Installer shell script, which size is 57M When inspect that script head script root@home-pc:/usr/local/src# head yEd-3.11.1_32-bit_setup.sh #!/bin/sh ...
2
votes
2answers
115 views

Awk not rendering any result

My goal is to get the file created in the current month in a directory. It seems that the command is correct but not rendering any result: Date=`date '+%b'` echo $Date Oct ls -l | awk -v d="$Date" ...
2
votes
2answers
736 views

setting variables inside subshell when using <<

I am using the following method in order to pass commands into a subshell that is started by "newgrp". #!/bin/csh echo "Before newgrp" /usr/bin/newgrp users <<EONG echo "hello from within ...
2
votes
2answers
10k views

What is the meaning of $* in a shell script? [duplicate]

In a shell script file i saw "$*", what does it mean and when we have to use it?
2
votes
2answers
722 views

Script to delete text files

I was trying to make a script that searches for all ASCII text files in the directory that you point out and after that writes the path of every file to a text file. After that it's supposed to show ...
3
votes
4answers
2k views

Align text to center with padding on both sides

Is there an easy way to align text to the center with padding on both sides, with the column width being the longest line from the input? For example, this: aaa bbbb c ddddd ee will turn into this ...
3
votes
5answers
692 views

Delete all files in directories except those whose path are listed in a file

Given the following files: data/A/a.txt data/B/b.pdf ... date/P/whatever.log ... data/Z/z.jpg I would like to delete all files in the data/A/, data/B/, ..., data/Z/ directories except those files ...
1
vote
4answers
460 views

Reusing a variable

I was breaking my head for a day still not successful. I have this script: #!/bin/ksh fname=$1 for batchname in $(grep -i "Processing batch" $fname | cut -d "'" -f2) do Batch_state=`grep -c -i ...
1
vote
2answers
2k views

Printing fields using awk

< pool.sam awk ' /./ {printf $1} {printf $7+1,"\t"} {printf $3,"\t"} { if($2 !=16) {print "\t", "+";} else {print "\t","-";} {printf $4,"\t" ,length($10)+$4, "\t", "1"} }' I am ...
0
votes
2answers
97 views

Eval command in unix [closed]

Can someone convert this code? I got this from the web. I am new on this and don't know how eval works. Originally, there is a parameter from a command that is either a plus (+) sign or a minus (-) ...
3
votes
2answers
216 views

Running commands after event based outputs

there are commands like iwevent or tcpdump -n src host x.x.x.x that send to the stdout some lines when something happens. Is there any form of running some command inmmediatly after a ...
1
vote
0answers
155 views

Intercepting packets with bash

I'm wondering if it's possible to detect a packet that comes from certain IP and port(suppose IP 1.1.1.1 and port 80) and has some specific information on it (suppose "<h1>Web ...
4
votes
3answers
214 views

What is this complex line of code doing?

I am trying to understand this line from a shell script. I know that $(..) means run the .. and insert its output where you find $() in a statement. But what is going on between those parenthesis? ...
3
votes
2answers
549 views

What is the meaning of if [ -n “$(which voltdb 2> /dev/null)” ];?

I have very basic linux skills and now am trying to parse some shell scripts. I see this line in one of the scripts: if [ -n "$(which voltdb 2> /dev/null)" ]; I know that /dev/null is the bit ...
2
votes
1answer
442 views

Merging folders with practically the same name but different casing

When digging around in the advanced settings in Dropbox I lost a folder. I only discovered this about a month later. I managed to get this folder back from Dropbox however the file structure of the ...
1
vote
1answer
2k views

using find in Bash Script and checking if file is present

var= "$(find . -name 'gen*.bt2')" if [ "$var" == "" ] then echo bad else echo great fi I get errors ./script.sh: line 4: ./gen.4.bt2 ./gen.rev.1.bt2 ...
2
votes
1answer
146 views

Any better method than this for sorting files by their creation date?

I needed to display a list of directories sorted by their creation date and I came up with this code snippet that I thought was kind of clever. Is there a more obvious way to do this that I'm missing? ...
0
votes
2answers
97 views

Run level script - Help

I want the following command to be ran, as soon as system boots. glances -s -P redhat & How to achieve that? I tried writing a run level script which didn't work as expected.
0
votes
3answers
2k views

Script to login to ssh twice

I need to login through ssh twice with a script and can't get it to work. This is what I have in my script file: #!/usr/bin/expect set login "user" set addr "address1" set addr2 "address2" set pw ...
5
votes
2answers
664 views

How do I run a script when I switch between keyboard layouts

I use more than one keyboard layout, and I would like to find a way to run a script when I switch between them. Is this possible? So far, I can assign a shortcut for a script like this: #!/bin/bash ...
1
vote
3answers
384 views

splitting the string in bash script

I am new to bash script. I am taking some input from user and checking details about that. Example: $HOME/Documents/test/one.txt I take the above string as an input and want to retrieve one.txt, I ...
12
votes
0answers
356 views

Should I use $* or $@? [duplicate]

Which one of $* or $@ is better to use (in array syntax,command line parameters, etc.) to avoid any bugs/problems in code? Or it does not make any difference?
2
votes
1answer
863 views

What's the problem with this script to change wallpaper?

I'm very new to Linux's world, so I would ask to forgive me for every stupid or too simple thing I will ask now. I installed Elementary OS from their website just yesterday. I wanted to change my ...
3
votes
2answers
192 views

Sourcing a shell script from within Emacs

I would like to source a shell script that changes my environment variables from within Emacs. That is, I would like the shell script to change the environment in which Emacs runs, and I would like to ...
-1
votes
2answers
86 views

Make a new sniffer [closed]

How can use the Linux-kernel to supervise what is going on, about the new connections, new ports, connected hosts? Like I will do a new sniffer. Which files should I monitor to know what is going ...
3
votes
1answer
5k views

How to assign result of sed to variable

Below is a complete copy of a demo I'm using to to figure out to get the sed command to get rid of the spaces in a persons name, and compress it down to not have spaces. Once this is done, I want to ...
1
vote
1answer
113 views

What is the use of ; in a single line command?

What does ; mean in single line scripts like this: while true; do sudo -n true; sleep 60; kill -0 '$$' || exit; done 2>/dev/null & Does it mean new line, or "next command"?
6
votes
1answer
195 views

What is the difference in these two bash environments?

I notice that with bash scripts, some people use a different shebang to the one that I'm used to putting at the top of my own. Can someone simplify the difference between these two? I use the ...
2
votes
1answer
2k views

How to write a Shell Script using the condition from a database

Consider this is the condition I need to check select count(*) from nm.table1 where column1 =true; Now it should come out of the db (PostgreSQL) and use IF THEN ELSE LOOP in the Unix Something ...
2
votes
1answer
132 views

Why does backslash get converted to space in echo statement if IFS='\'?

Why is \ is converted to space on setting IFS='\' var="'(]\\{}\$\"" IFS='\' echo $var # '(] {}$"
11
votes
2answers
9k views

Regular expression in bash script

This is my first time bash scripting so I'm probably making an easy mistake. Basically, I'm trying to write a script that gets the groups of a user, and if they are in a certain group, it will log ...
3
votes
2answers
370 views

Getting the complete command line that caused an ERR , while trap

How do I make trap to return the command that caused an ERR? $function err_handler() { echo "$0 caused the error"; } $ trap err_handler ERR $ grep -ci "failed" test4 &>/dev/null -bash caused ...
2
votes
2answers
467 views

Optimized way to list and delete files

I need to list and delete .php, .xml files. For this I am using find command. To list : find . -type f -name \*.php -print0 To delete : find . -type f -name \*.php -print0 | xargs -0 rm -r As I run ...
2
votes
0answers
199 views

Check via Shell-script if server currently streams via dlna

Currently I'm running uShare to stream videos from my home-server via DLNA to the TV. On the server there is also running a bash-script which checks if a user is connected via ssh or Samba. If this is ...
6
votes
2answers
1k views

How does this find command using “find … -exec sh -c '…' sh {} +” work?

@StephaneChazelas posted the following solution to this Q&A: Having some trouble using “find -exec {} +”. $ find . -iname "*.extension" -exec sh -c ' exec <command> "$@" <additional ...
0
votes
1answer
4k views

Why does scp say “No such file”?

I have a bash script that uses scp to copy a file from my machine to another. The script keeps on exiting after I enter the SSH password with the error: <filename>: No such file or directory ...
1
vote
5answers
2k views

Print nth line before the matched line, Matching line and nth line from the matched line

I want Print nth line before the matched line, Matching line and nth line from the matched line where "n" is greater than 2. Here's an example of my data file (the line numbers below are not part of ...
1
vote
2answers
248 views

Why does this not work when the load average exceeds 1?

I have been testing this script and its behavior has been odd. The script should generate notifications whenever the load average exceeds a specified limit. Whenever I pass a CPU_LOAD_LMT >=60, no ...
1
vote
1answer
1k views

Error out shell script if plsql program fails

In the shell script, I am calling a PLSQL stored procedure sqlplus -s <<EOF $v_fcp_login set head off feed off serverout on size 1000000 exec ...
0
votes
1answer
486 views

List of special characters in the shell [closed]

I am not sure what they are called, but where could I find a list of wild cards? I see things like: $f %s $1 Is there a definitive list for what each one represents?
4
votes
1answer
1k views

Scoping variables in ksh

In ksh, I have two variables with the same name , one global , other one is local to a function #!/bin/ksh LOG_FILE=lf function exec_script { local LOG_FILE=f print $LOG_FILE } exec_script ...