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

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2
votes
2answers
119 views

selecting specific string in a field

I have this file: N104 F1810 N104 F3810 N104 F810 N104 F305 and a script to grep an input. Script: enter input read input cat file | grep $input when I input “810”, I get the ...
2
votes
4answers
2k views

SSH exits after quit case in bash script

So I have the following standard script: #!/bin/bash PS3='Please enter your choice: ' options=("option 1" "Option 2" "Option 3" "Quit") select opt in "${options[@]}" do ...
2
votes
2answers
3k views

For loop for renaming files with prompt for each filename

I have to convert multiple video files in a folder. I have to rename each one of them but I need the script to prompt me to write a custom name for each filename. Here is what I've got so far: First ...
1
vote
2answers
418 views

Shell: Break both if and for loop at once

Shell: Break both if and for loop at once. My script: ip to name resolve code IP=192.168.27.191 hostNameChecker() { if [ `getent hosts $1 | wc -l` -ne 0 ];then HOST_NAME=`hostname` ...
2
votes
0answers
1k views

Script stops command in it with exit 0

When I write a bash script similar to this on RHEL 6, if [ "$2" = "" ] ; then echo vip.start: ERROR: no NIC specified echo vip.start: Need IP and base interface name exit 1 fi case "$1" ...
2
votes
3answers
11k views

Loop over a file and read values from two columns into variables

I have a file (data.dat) which contains 3 columns. I want to read in two of them with the shell script and fill the contents into a template file. The file looks like this: 12 180 2390 14 177 2210 16 ...
2
votes
2answers
2k views

what is >> symbol and >& in unix/Linux? [duplicate]

I have a CRONTAB entry as below. Can someone tell me what the below statement is exactly doing? 1 0 * * * /vol01/sites/provisioning/MNMS/45627/45627.sh1 >> ...
0
votes
1answer
326 views

Change date after SSH login in shell script

I have to change the date after an SSH login into machine, but I am not able to change it. Here is the script I have written: #!/bin/bash ENVIRONMENT_LIST=environment_ip_list USERNAME=root declare ...
3
votes
2answers
2k views

How to safely reverse dns lookup on ip in a shell script

I'm trying to find out how to take in a hostname and pop out an ip address (reverse dns lookup). I came up with this but I'm not too sure it's safe across different linux distros: nslookup $ip|grep ...
1
vote
1answer
1k views

How to figure out where a link gets redirected

I currently working on a script that updates a file. The file has several versions. The important ones have static links. These get redirected to the actual file which then gets downloaded using wget. ...
1
vote
2answers
2k views

To configure script to send email only when diff command gives a difference

I'm new to the world of scripting and and currently using a script to perform a health check on the san devices that I manage. The script is simple and redirects output of commands to a current file ...
1
vote
3answers
546 views

Which cmd is the best for determining the OS' word size (32/64)-bit? [duplicate]

I need to find my OS (not hardware) is 32-bit / 64-bit. Which command is best? uname -p uname -i uname -m arch All the above commands returns the same answer: On 32 bit systems: i686/i386 On ...
13
votes
1answer
1k views

How does a fork bomb work?

WARNING DO NOT ATTEMPT TO RUN THIS ON A PRODUCTION MACHINE In reading the Wikipedia page on the topic I generally follow what's going on with the following code: :(){ :|:& };: excerpt of ...
2
votes
1answer
177 views

Linux: I need to create installer for my own application using shell script

Linux: I need to create installer for my own application using shell script. I need to distribute my application as installer without GUI and also not as rpm's or any other packages. My application ...
13
votes
1answer
11k views

Empty the contents of a file

I am aware of three methods to delete all entries from a file. They are >filename touch filename filename < /dev/null Of these three I abuse >filename the most as that requires the ...
5
votes
3answers
1k views

Cron to not run on specific day but all other days

I have a cron setup to execute a bash script daily at 10pm. I have another cron setup to run monthly on the 1st of the month. Both crons launch a bash script, and the only different in the bash script ...
1
vote
4answers
4k views

Match multiple regular expressions from a single file using awk

I'm trying to parse a HTML file using shell scripting. There are 4 different regular expressions that i need to catch: name= , age= , classs= , marks=. Using grep "name=\|age=\|class=\|marks=" ...
2
votes
4answers
3k views

FTP bulk download and rename

First of all: Why I'm trying this? Because we need to download some files AND rename to shorten ones with date "stamps". The remote files have really huge filenames and it's not an option to ...
0
votes
2answers
625 views

Unix: How to Test Ip Address is resolved to name

Unix: How to Test ip Address is resolved to name. I need to check whether ip address can be resolved to name using DNS entry via shell script. Code: DNS_Lookup() { LOOKUP=$(nslookup $1) ...
2
votes
3answers
3k views

How is it possible to sort ps command's CPU field?

I'm trying to make a small command that will find the processes that use the most CPU power. Firstly, I use ps aux > file.txt and then cut -c 16-20 file.txt | sort -n | tail -5. The result I get ...
1
vote
1answer
461 views

Execute command supplied by function parameters

I'm trying to create a function method in a bash script that executes a command which is supplied to the method by the paramters. Meaning somethings like this: special_execute() { # Some code ...
3
votes
5answers
257 views

Comparing Indices of two strings

I have two double quoted strings of same length, that look like this: "$con" - (consists of spaces and *'s): * ****** *** ** * ** and ...
2
votes
1answer
13k views

Concatenating two variables with an underscore [duplicate]

Alright. I need to concatenate two variables to create a filename that has an underscore. Lets call my variables $FILENAME and $EXTENSION where filename is read from a file. FILENAME=Hello ...
1
vote
2answers
112 views

Backing up a large file

I have a test running which crashes. I need to find out how far it reached before crashing. It will restart again after crashing and wipe the log file. This wiping takes 10 minutes though. So If I'm ...
1
vote
2answers
301 views

What is sourcing my shell script?

I have a .zshrc and a .zshenv in my home directory. I added a new command to my .zshenv that I discovered was being run at least 3 times. I realized that I was accidentally sourceing it from the ...
1
vote
3answers
101 views

How to transform text such that each output line starts with the block's title?

I need to make a script to transform the following: Name = x:y Z = a:b.c Z1 = a1:b1.c1 End Name=x1:y1 Z2 = a2:b2.c2 Z3 = a3:b3.c3 Z4 = a4:b4.c4 End Name = l:k s = w:e.v End into: x:y Z a:b.c ...
0
votes
2answers
400 views

sed with auto escape character [duplicate]

CommentAppend() { # Comment line and append line below commented line local comment="$1" # search this line and comment it local append="$2" # Append this line below commented ...
6
votes
5answers
6k 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 ...
0
votes
1answer
241 views

How does this bash statemnet test “.$TOMCAT_USER” = . && TOMCAT_USER=tomcat work?

I am trying to understand the tomcat daemon.sh script which contains a bunch of lines along the lines test ".$TOMCAT_USER" = . && TOMCAT_USER=tomcat I figured out that test ".$TOMCAT_USER" = ...
3
votes
2answers
357 views

Writing scripts that use different commands in different shells [duplicate]

How can I write a script that is shell independent? I want to be able to run one script which will run in ksh, sh and bash. For example: If I have a line in my script like whence ls which will run in ...
4
votes
2answers
655 views

Exiting out of an infinite reboot loop in startup (rc.local)

I am creating a startup script (called from rc.local) in Debian Squeeze. The startup script checks for a variable value from a file, decrements the variable and writes it back to the file, then if the ...
1
vote
1answer
191 views

How achieve variable indirection (refer to a variable whose name is stored in another variable) in tcsh

I'm trying to do the following: set a = kitten set temp_kitten = purr echo ${temp_$a} I want the echo command to return "purr". The overall idea is that I have a bunch of variables in an array and ...
4
votes
2answers
279 views

Remove all lines except D

I have scenario where my three huge files Test.txt , Test1.txt and Test2.txt has following details. H||||||||||||||||||||||| D|||||||||||||||||||||||| D||||||||||||||||||||||| H||||||||||||||||||||| ...
1
vote
1answer
258 views

How do I start smbclient from a script in Linux?

I want to be able to quickly start smbclient to a specific directory without typing or copying it to the shell command line, but just sticking it in a script doesn't seem to work... #!/bin/csh ...
1
vote
1answer
2k views

How does this su -c “…” command seem to pass two commands instead of one?

I am trying to understand the script below and I am confused about the su line. I understand the postgres command line arguments. when I do man su the manual says -c, --command=COMMAND ...
0
votes
1answer
87 views

Problem with small bash script

I often run find in my code projects when I make a change somewhere and I have to find where it impacts other pieces of code, so I thought about writing a very small script to make this easier, call ...
3
votes
2answers
4k views

Shell Script - syntax error near unexpected token `else'

With the following shell script, why I am getting errors syntax error near unexpected token `else' Shell Script echo "please enter username" read user_name echo "please enter password" read -s ...
7
votes
5answers
20k views

Add lines to the beginning and end of the huge file

I have the scenario where lines to be added on begining and end of the huge files. I have tried as shown below. for the first line: sed -i '1i\'"$FirstLine" $Filename for the last line: sed -i ...
1
vote
1answer
594 views

Error not a valid identifierd when executing shell script [duplicate]

I have the following shell script in order to connect to database and do some tasks. echo Please enter userid: read USER_NAME echo "Please enter password:" read -s PASS SID=${ORACLE_SID} if [ ...
3
votes
4answers
3k views

How do I select files in a bash script that do not have an extension?

Let's say I have files xinitrc, alphabetsoup, ieat.pie in the current directory. Need a bash script to select only xinitrc and alphabetsoup.
5
votes
1answer
106 views

Is it possible to create sticky redirection from stdout/stderr

Consider such code: echo hello >> log.txt echo world >> log.txt I execute command with stdout redirection. Is it possible to create sticky redirection? Something like this: redir ...
2
votes
6answers
7k views

Using cut/awk/sed with two different delimiters

I have the following cases: case@test.com case_1_2@test.com case_1@test.com I'm trying to convert these to case@test.com case@test.com case@test.com So it should remove everything from ...
2
votes
1answer
127 views

Redirecting an active port

Environment: Web server that requests pages on a specific port from an application server. Problem: If a page request comes into the application server during the restart of a certain web application ...
2
votes
4answers
5k views

Shell script to check for the presence of one or more files with a specific extension?

I want to write a script to find a file with specific extension.this much i have done: #!/bin/bash file="/home/Savio/Dsktop/check/*.csv" file1="/home/Savio/check/*.txt" if [[ -f "$file" && -f ...
14
votes
1answer
23k views

How can I execute local script on remote machine and include arguments?

I have written a script that runs fine when executed locally: ./sysMole -time Aug 18 18 The arguments "-time", "Aug", "18", and "18" are successfully passed on to the script. Now, this script is ...
2
votes
3answers
4k views

Using a reference to a bash string variable in sed

I'm a relative Linux novice. Suppose that I have a text file a.txt that contains the following text: A B C Now, if I want to change the text on line 2 (which contains B), I can use the following ...
1
vote
1answer
213 views

Is there a way to see which process invoked a shell script?

Is there a possibility so see from some unix log file what process have invoked a bash/ksh shell script or is this shell script invoked manually from command line? So is there some log file which ...
4
votes
4answers
1k views

Why cat, grep and other commands can't understand files starting with minus sign? [duplicate]

If I have a file which name starting with single or several minus sign, for example --1 it can't be used as a parameter of many commands. Even if I run cat --1 instead of file content I get ...
0
votes
1answer
107 views

Converting a loop of code to function

I want to retry a command for 5 times with an interval of 20 seconds. I want this command to be passed as a method parameter. How to do it? And once the function is written how to pass the value to ...
4
votes
7answers
2k views

how to share environment variables between shells like globals related to a master pid?

So, I need to share environment variables between shells, and that the changes on the variables be promptly recognized by all shells, like global variables. But they must be related to a master pid, ...