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

learn more… | top users | synonyms (2)

9
votes
1answer
20k views

sudo: unable to execute ./script.sh: no such file or directory

I'm stumped. I have a script in my /home directory which is executable: [user@server ~]$ ll total 4 -rwx------ 1 user user 2608 Jul 15 18:23 qa.sh However, when I attempt to run it with sudo it ...
9
votes
6answers
10k views

Find biggest files or directories

Which command will print the sizes of all files and directories in the tmp directory (including hidden ones) and sort them by sizes from largest to smallest in human readable format (e.g. 2 GB)? The ...
9
votes
2answers
1k views

Are quotes needed for local variable assignment?

Can I safely omit quotes on the right side of a local assignment? function foo { local myvar=${bar} stuff() } I'm mainly interested in bash, but any info on corner cases in other shells are ...
9
votes
1answer
362 views

Know which process does I/O without iotop

On Linux, I want to know which process uses my disk I/O bandwith. I know I can use iotop but I have a machine where, for various reasons, iotop cannot be installed. How can I manually get that ...
9
votes
3answers
967 views

Is there a way to convert a zip to a tar without extracting it to the filesystem?

Is there a way to convert a zip archive to a tar archive without extracting to a temporary directory first? (and without writing my own implementation of tar or unzip)
9
votes
1answer
2k views

Are dash, ash and sh script 100% compatible?

I wanted to know whether scripts written for dash, ash, and sh are 100% compatible? Are there any added features to dash or ash, or syntax change? From what I heard, ash is a direct descendant of ...
9
votes
2answers
2k views

Check bash/shell script dependencies

Is there a method/command to check for the dependencies of a bash script? In other words, a response to this question : Which libraries should a user install to run the script? I can do this ...
9
votes
4answers
210 views

Script to extract selected entries from a bibtex file

I have a large bibtex file with many entries where each entry has the general structure @ARTICLE{AuthorYear, item = {...}, item = {...}, item = {...}, etc } (in some cases ARTICLE might be a ...
9
votes
2answers
470 views

Using a shell script as a virtual printer

I have a shell script that takes a PDF file as an argument and prints it with additional printer specific options. How can I add this script as a virtual printer that can be selected from the GUI? ...
9
votes
2answers
609 views

Cache all gpg subkey passwords at once? Prevent need for multiple gpg password entry?

Can I enter my gpg password just once and unlock all my sub keys (signing, decryption, authentication)? At the moment, I need to enter my gpg password three times (for signing, for decryption, for ...
8
votes
8answers
934 views

Grep for pattern at start or middle of a line

I'll start by saying that I think this problem is a little less innocent than it sounds. What I need to do: check for a folder within the PATH environment variable. It could be at the start or ...
8
votes
3answers
8k views

Prompt user to login as root when running a shell script

The problem I am getting is, when I enter the command, su - root at the beginning of my shell script file, it prompts the user to enter the password and then does NOT continue with the rest of the ...
8
votes
7answers
4k views

cron Vs. sleep - which is the better one in terms of efficient cpu/memory utilization?

The Case: I need to run some commands/script at certain intervals of time and for this I have two options - 1. set up a cron-job or, 2. implement a loop with sleep in the script itself. Question: ...
8
votes
5answers
3k views

Bash CD up until in certain folder

I do a lot of work in Magento, and so do a lot of the people I work with, and it gets annoying to have to type: cd ../../../../../../ To only find you're still a few directories from your root ...
8
votes
2answers
329 views

Why does printf print more arguments than expected?

Why is this shell script printing inputs twice? I expected the script to ignore the inputs after 5. Script: #! /bin/bash echo "Enter 5 words : " read a b c d e printf "> %s %s %s %s %s <" ...
8
votes
2answers
13k views

Extracting a string, according to a pattern, in a bash script

In bash, suppose that I have a string strname: strname="ph7go04325r" I would like to extract the characters between the first "3" character and the last "r" character in strname, saving the result ...
8
votes
4answers
11k views

How to extract logs between two time stamps

I want to extract all logs between two timestamps. Some lines may not have the timestamp, but I want those lines also. In short, I want every line that falls under two time stamps. My log structure ...
8
votes
5answers
7k views

Compare two files with first column and remove duplicate row from 2nd file in shell script

I will ask my question with an example. I have 2 files: File #1: 118D FC300_R5_TP FX.B 32775 2112 6 2038 6 2112 0 118E FC300_R5_TP FX.B 32775 2136 7 ...
8
votes
1answer
33k views

In a bash script, using the conditional “or” in an “if” statement

This question is a sequel of sorts to my earlier question. The users on this site kindly helped me determine how to write a bash for loop that iterates over string values. For example, suppose that ...
8
votes
2answers
1k views

How to non-invasively test for write access to a file?

In a shell script, how do I easily and non-invasively test for write access to a file without actually attempting to modify the file? I could parse the output of stat, but that seems really complex, ...
8
votes
2answers
2k views

Piping data to a process's stdin without causing EOF afterward

I have an executable that starts a user-interactive shell. I would like to, upon launch of the shell, inject a few commands first, then allow the user to have their interactive session. I can do this ...
8
votes
3answers
12k views

getopt, getopts or manual parsing - what to use when I want to support both short and long options?

Currently I'm writing a Bash script which has the following requirements: it should run on a wide variety of Unix/Linux platforms it should support both short and (GNU) long options I know that ...
8
votes
2answers
983 views

Measuring time within a script

This thread shows how to measure the time it takes to run a script. In my case, I am interested in measuring time between two points within a script. Here is an example of how I would like to use ...
8
votes
2answers
10k views

Remove end of line characters from stdout? Multiple lines into a single line

I have a script which outputs the following text. This is the output from a Netopia 2210-02 ADSL2 modem. ADSL Line State: Up ADSL Startup Attempts: 1 ADSL Modulation: DMT ADSL Data ...
8
votes
1answer
947 views

How to append multiple lines to a file with bash, with “--” in front of string

Question very similar to How to append multiple lines to a file with bash but I want to start the file with --, and also append to the file, if possible. printf ...
8
votes
3answers
5k views

Loop through the lines of two files in parallel [closed]

The object of the script I'm making is to compare two series of files. The file names are themselves stored into two separate files, one path per line. My idea is to have two while read loops, one for ...
8
votes
2answers
455 views

Multiple shebangs in a single bash file

I have a script from other person which has a look (note: it's a single file): #!/bin/bash some commands some commands #!/bin/bash some commands some commands #!/bin/bash some commands some ...
8
votes
7answers
3k views

How to detect the desktop environment in a bash script?

I am writing a bash script that needs to know which desktop environment (XFCE, Unity, KDE, LXDE, Mate, Cinnamon, GNOME2, GNOME3,... ) is running. How can I obtain that information?
8
votes
4answers
5k views

exit shell script from a subshell

Consider this snippet: stop () { echo "${1}" 1>&2 exit 1 } func () { if false; then echo "foo" else stop "something went wrong" fi } Normally when func ...
8
votes
3answers
5k views

Diff, show modified line from right file only

I have file a and b and I would like to output lines of b that changed since it was cloned from a. Just the modified lines, no surrounding context, no diff offset marks. How can I do that using shell ...
8
votes
1answer
1k views

Using inotify to monitor a directory but not working 100%

I have written a bash script to monitor a particular directory /root/secondfolder/: #!/bin/sh while inotifywait -mr -e close_write "/root/secondfolder/" do echo "close_write" done When I ...
8
votes
1answer
5k views

Trap, ERR, and echoing the error line

I'm trying to create some error reporting using a Trap to call a function on all errors: Trap "_func" ERR Is it possible to get what line the ERR signal was sent from? The shell is bash. If I do ...
8
votes
5answers
2k views

How to run part of a script with reduced privileges?

I have the following problem: On every machine running Postgresql there is a special user postgres. This user has administrative access to the database server. Now I want to write a Bash script that ...
8
votes
2answers
398 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?
8
votes
3answers
5k views

whiptail or dialog

I am going to create script which will use user input, so I decided to use whiptail, but little bit confuse that which one is portable and will work in ubuntu 10.x and higher and CentOs5.x and higher. ...
8
votes
1answer
294 views

Bash wildcard to match exactly n characters

Is there a wildcard in bash to match exactly 5 characters, shortening a pattern like ?????
8
votes
3answers
10k views

Creating a Bash script that will execute a program and if it exits without crashing, will run it again

I'd like to know the easiest way of creating a bash script that will run an app in MacOSX (it's a UNIX based system so I assumed this was the right place). wait for the program to exit. If the exit ...
8
votes
1answer
2k views

How to continue a script after it reboots the machine?

I'm writing a shell script in bash. At some point in the script, it detects that the machine needs to be rebooted before continuing. It issues: sudo reboot When the machine comes back up, there ...
8
votes
5answers
10k views

Print Matching line and nth line from the matched line

I am trying to print the matched line and the 4th line from the matched line (line containing the expression I am searching for). I have been using the following code: sed -n 's/^[ \t]*//; /img ...
8
votes
3answers
17k views

How to set global environment variables at boot through a script, and have them available for an application that runs before login?

I have a service that runs at boot, and in that service it calls a bash script in the background that exports some environment variables. The problem I'm having is that those environment variables ...
8
votes
3answers
1k views

How to enable safeguards for CPU temperature

My desktop has a nasty habit. When I have several high intensity applications running and my CPU is at maximum usage for a period of time, the core temperature rises and my computer auto-shuts off. ...
8
votes
4answers
315 views

Do you prefer bash scripts or aliases for shortcuts?

I have a ~/bin directory (which is on my PATH) where I store a lot of little 1 or 2 line scripts. Some of them just cd into a directory and run a command on a file, like vim or something. But I also ...
8
votes
1answer
9k views

Executing commands with ssh and shell script using variables on a remote machine

I'd like to execute a command and script located on a remote machine with a script on a local machine. I know it's possible to execute these kind of commands with ssh, so I made: #!/bin/bash ssh ...
8
votes
1answer
353 views

Are [ “$VAR” = “” ] and [ -z “$VAR” ] always equivalent?

My code looks something like this: VAR="" while [ -z "$VAR" ]; do VAR=$( command | grep "important_string" ) done So I want to poll the output of command, until the important_string appears and ...
8
votes
1answer
1k views

what is the zsh equivalent of bash's export -f

So I started using zsh. I like it all right. It seems very cool and slick, and the fact that the current working directory and actual command line are on different lines is nice, but at the same time, ...
8
votes
3answers
523 views

POSIX compliant way to work with a list of filenames possibly with whitespace

I have seen Bash scripting guides suggesting the use of array for working with filenames containing whitespace. DashAsBinSh however suggests that arrays are not portable so I am looking for a POSIX ...
8
votes
0answers
214 views

how to get exit status from the command before the last [duplicate]

I have solaris machine ( solaris 10 ) please Look on the following simple commands (haconf -makerw | grep -iq "Cluster already writable") # haconf -makerw VCS WARNING V-16-1-10364 Cluster ...
7
votes
7answers
834 views

Slick one-liner to convert a list like “1: 2, 3, 4, 5” to “1.2, 1.3, 1.4, 1.5”

Let's say I have a file that looks something like this: 23: a, b, c, d 24: b, d, f 25: c, g and I want to get output like this: 23.a 23.b 23.c 23.d 24.b 24.d 24.f 25.c 25.g Of course it's not ...
7
votes
4answers
27k views

Storing output of command in shell variable [duplicate]

I have an operation using cut that I would like to assign result to a variable var4=echo ztemp.xml |cut -f1 -d '.' I get the error: ztemp.xml is not a command The value of var4 never gets ...
7
votes
1answer
2k views

Determine if Git working directory is clean from a script

I have a script which runs rsync with a Git working directory as destination. I want the script to have different behavior depending on if the working directory is clean (no changes to commit), or ...