grep – command used for the patter matching it have many useful options
-i: to make case-insensitive search
-r: search through the file in dire recursively
– l: print the name of the file with matching string
-c: print the counts of match
-n: numbers the matching lines in the output
-v: it's like not condition, print the reverse of the condition
sed – its read the input lines, run script on them, and writes them to stdout. This command is good for the string replacement and editing of the files.
Both these commands can be used with regex for the pattern matching.
>> grep -nv ^# \| ^$ /etc/services |less
# will list all the lines from the file with do not start with *#* and ends with an empty line.
>>sed ``s/UNIX/LINUX` file.txt
# sed command will replace the occurrence of the *UNIX* word with the *LINUX*
Today was the day of basic File Management, Pipes, and Redirects.
So let's jump to the command's
mkdir – create a directory for you, -p will create the parent directory if it does not exist.
rmdir – remove the empty directory
rm – remove the files and directory with -r.
pushd & popd – this one is the new command I came across, it let you save the previous command and you can pop that command with popd when you require. Dirs let you list down the directories you can pop back too.
file – tells you about the format of the file
?, * – these are the wildcards which help in pattern matching, '*' for any number of character and whereas ? for only one character
| – called as pipe, it takes the output of one program and gives as an input to another program
Redirection (<, >) – < this indicates to file to read input from, > this indicates the file to write output to.
>> – Appends the output to the end of the file, If the file does not exist it creates a new one.
File Descriptors – Standard Input(0), Standard Output (1), Standard Error (2), make sure to check the example below to see how you can use them
xargs- it read a text and pass them as input to the following command
tee – is a combination of > and | and let you copy data from the input to the output or a file
Now let see these commands in action
>> mkdir -p chess/pieces/board # create an directory for you.
>> rmdir -p chess/pieces/board # will delete whole path if no other file or dir exist
>> pushd /media/USB # will let you save this path
... # any command you run b/w
>> popd # this will get you back to the pushed path
>> dirs # list all the dir path saved
~/bash-trail ~ / ~/Code/tranzact ~/bash-trail/program
>> file shopping_list
shopping_list: ASCII text
>> whoami | rev # will reverse the output from the *whoami* output
keepdnas
>> last > last-login.txt # will save the output of login user to the file
>> wc < last-login.txt # will pass the text from the file as input to the *wc* command
>> program 2> file # will write the Standard error from the program to the file. **File Descriptor**
>> find /media/USB | xargs -l 3 rm -f # this will pass files for USB dir and xargs will pass the 3 filenames at a time to remove them.
>> last | tee everyone.txt | grep bob > bob.txt
# To save details of everyone’s logins and save Bob’s in files also.
Today run through the commands to process the Text streams from the shell.
less – command let you show less content from the file you are viewing.
sort – helps you sort the output, -f let you do sort case-insensitive and -n numerical sort.
cut – help to select the fields(-f)/character(-c)
fmt – format the output of the file, you can specify the width with -w
tac – similar to the cat command but in reverse
sed- this command use to process each line of file with a script
let see these command in action
>> less hello.txt
Hello World
THis is a text file
hello.txt (END)
>> cat shopping_list
cucumber
bread
fish fingers
>> sort shopping_list
bread
cucumber
fish fingers
>>date
Thu Jul 9 00:21:17 IST 2020
>>date | cut -d " " -f1
Thu
>>cat COPYING | less
The GNU General Public License is a free, copyleft license for
software and other kinds of works.
The licenses for most software and other practical works are designed
>> cat COPYING | less | fmt -w 30
The GNU General Public
License does not permit
incorporating your program
>>cat copybump.py
#! /usr/bin/env python3
import datetime
import os
import re
import stat
import sys
...
if __name__ == '__main__':
do_walk()
>> tac copybump.py
do_walk()
if __name__ == '__main__':
...
import sys
import stat
import re
import os
import datetime
#! /usr/bin/env python3
>> sed -f spelling.sed < report.txt > corrected.txt # correct the spellling mistake in report.txt and output the correct text in corrected.txt
This post and the continuing post will be post/notes to share my journey of going through the shell to brush the commands which I forget and to learn some new ones.
So here one or more things I learned today.
* !! – will show you the previous command.
* ! String- show's the last command with the given string.
* !$– will give the last argument of the previous command
* !^ – will give you the first argument of the previous command
* ^String^replacement- will replace the first occurrence of the * String* with the replacement string.
* Ctrl + A – will get you to the start of the line.
* Ctrl + E – will get you to the end of the line.
* Ctrl + D – will delete the current character, even can close your shell session :).
* For loop – yup we can write for loop to certain repetitive actions.
* Locate – can help you to search for the file/s in the drive.
* file – it not only help you with the file search just not based on the name but has many options to perform on the result and you can use regex for the file search also.
Now let's dive into some cool example
>> ls
...
>> clear
>>!! # will refer to the previous command
>> clear
>> !l # refers to the previous command start with a given string in our case `l`
>> ls
>> cd Documents
>> echo !$ # will refer to the *Documents* args from the previous command, same will be the case with *!^* which refer the first args of the previous command
>> ls
>> echo !$
>> echo ls
>> echo Documents
>>for file in *; echo ${file}; done # try to run this in the shell to see the output