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Update Readme (#1) 

* Add which command

* Add syantax highlighting
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Zeeshan Ahmed 2017-04-01 15:13:06 +05:00 committed by Adnan Ahmed
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@ -16,7 +16,7 @@
This is first line that you will in bash script files called `shebang`. The shebang line in any script determines the script's ability to be executed like an standalone executable without typing sh, bash, python, php etc beforehand in the terminal.
```
```bash
#!/bin/bash
```
@ -25,11 +25,11 @@ This is first line that you will in bash script files called `shebang`. The sheb
### a. `export`
Displays all environment variables and if you want to get detail of specific variable then use `echo $VARIABLE_NAME`
Syntax:
```
```bash
export
```
Example:
```
```bash
$ export
SHELL=/bin/zsh
AWS_HOME=/Users/adnanadnan/.aws
@ -44,16 +44,28 @@ $ echo $SHELL
### b. `whereis`
Finds out where a specific binary is on your system.
Syntax:
```
```bash
whereis `name`
```
Example:
```
```bash
$ whereis php
/usr/bin/php
```
### c. clear
### c. `which`
Locate a program file in the user's path. This command will prints full path of the executable(s). It does this by searching the directories listed in the environment variable PATH.
Syntax:
```bash
which `program_name `
```
Example:
```bash
$ which php
/c/xampp/php/php
```
### d. clear
Clears content on window
## 1.1. File Commands
@ -86,7 +98,7 @@ Clears content on window
### a. `ls`
Lists your files. It has a lot of options like `-l` lists files in 'long format', which contains the exact size of the file, who owns the file and who has the right to look at it, and when it was last modified. `-a` lists all files, including hidden files. For more information on this command check this [link](https://ss64.com/bash/ls.html)
Syntax:
```
```bash
ls `option`
```
Example:
@ -105,39 +117,39 @@ drwxr-xr-x 17 adnan staff 578 Mar 27 23:36 .git
### b. `touch`
Creates or updates your file
Syntax:
```
```bash
touch `filename`
```
Example:
```
```bash
$ touch trick.md
```
### c. `cat`
Places standard input into file. Means that it opens the file in terminal for you to edit
Syntax:
```
```bash
cat > `filename`
```
### d. `more`
Shows the first part of a file (move with space and type q to quit)
Syntax:
```
```bash
more `filename`
```
### e. `head`
Outputs the first 10 lines of file
Syntax:
```
```bash
head `filename`
```
### f. `tail`
Outputs the last 10 lines of file. Use `-f` to output appended data as the file grows
Syntax:
```
```bash
tail `filename`
```
@ -145,7 +157,7 @@ tail `filename`
### g. `mv`
Moves a file from one location to other
Syntax:
```
```bash
mv `filename1` `filename2`
```
Where `filename1` is the source path to the file and `filename2` is the destination path to the file.
@ -153,7 +165,7 @@ Where `filename1` is the source path to the file and `filename2` is the destinat
### h. `cp`
Copies a file from one location to other
Syntax:
```
```bash
cp `filename1` `filename2`
```
Where `filename1` is the source path to the file and `filename2` is the destination path to the file.
@ -163,25 +175,25 @@ Removes a file. But if you will apply this command on a directory directory, it
`rm: directory: is a directory`
So in order to remove directory you have to pass `-rf` to remove all the content of the directory recursively
Syntax:
```
```bash
rm `filename`
```
### j. `diff`
Compares files, and shows where they differ
Syntax:
```
```bash
diff `filename1` `filename2`
```
### k. `wc`
Tells you how many lines, words and characters there are in a file
Syntax:
```
```bash
wc `filename`
```
Example:
```
```bash
$ wc demo.txt
7459 15915 398400 demo.txt
```
@ -190,46 +202,46 @@ Where `7459` is lines, `15915` is words and `398400` is characters.
### l. `chmod`
Lets you change the read, write, and execute permissions on your files
Syntax:
```
```bash
chmod -options `filename`
```
### m. `gzip`
Compresses files
Syntax:
```
```bash
gzip `filename`
```
### n. `gunzip`
Un-compresses files compressed by gzip
Syntax:
```
```bash
gunzip `filename`
```
### o. `gzcat`
Lets you look at gzipped file without actually having to gunzip it
Syntax:
```
```bash
gzcat `filename`
```
### p. `lpr`
Print the file
Syntax:
```
```bash
lpr `filename`
```
### q. `lpq`
Check out the printer queue
Syntax:
```
```bash
lpq
```
Example:
```
```bash
$ lpq
Rank Owner Job File(s) Total Size
active adnanad 59 demo 399360 bytes
@ -239,25 +251,25 @@ active adnanad 59 demo 399360 bytes
### r. `lprm`
Remove something from the printer queue
Syntax:
```
```bash
lprm `jobnumber`
```
### s. `grep`
Looks for text inside files. You can use grep to search for lines of text that match one or many regular expressions, and outputs only the matching lines.
Syntax:
```
```bash
grep `pattern` `filename`
```
Example:
```
```bash
$ grep admin /etc/passwd
_kadmin_admin:*:218:-2:Kerberos Admin Service:/var/empty:/usr/bin/false
_kadmin_changepw:*:219:-2:Kerberos Change Password Service:/var/empty:/usr/bin/false
_krb_kadmin:*:231:-2:Open Directory Kerberos Admin Service:/var/empty:/usr/bin/false
```
You can also force grep to ignore word case by using `-i` option. Also `-r` can be used to search all files under the specified directory like
```
```bash
$ grep -r admin /etc/
```
And `-w` to search for words only.
@ -275,24 +287,24 @@ And `-w` to search for words only.
### a. `mkdir`
Makes a new directory
Syntax:
```
```bash
mkdir `dirname`
```
### b. `cd`
Moves you from one directory to other. If you just run
```
```bash
$ cd
```
Then it will moves you to home. Also this command accepts an optional `dirname`, which if provided will moves you to that directory.
```
```bash
cd `dirname`
```
### c. `pwd`
Tells you in which directory you currently are
Syntax:
```
```bash
pwd
```
@ -334,12 +346,12 @@ pwd
### a. `ssh`
ssh (SSH client) is a program for logging into a remote machine and for executing commands on a remote machine.
Syntax:
```
```bash
ssh user@host
```
This command also accepts an option `-p` that can to used to connect to specific port.
Syntax:
```
```bash
ssh -p `port` user@host
```
@ -352,7 +364,7 @@ Allows the current logged user to change his password
### d. `quota`
Shows what your disk quota is
Syntax:
```
```bash
quota -v
```
@ -371,21 +383,21 @@ Displays who is online
### i. `finger`
Displays information about user
Syntax:
```
```bash
finger `username`
```
### j. `uname`
Shows kernel information
Syntax:
```
```bash
uname -a
```
### k. `man`
Shows the manual for specified command
Syntax:
```
```bash
man `command`
```
@ -395,35 +407,35 @@ Shows disk usage
### m. `du`
Shows the disk usage of the files and directories in filename (du -s give only a total)
Syntax:
```
```bash
du `filename`
```
### n. `last`
Lists your last logins of specified user
Syntax:
```
```bash
last `yourUsername`
```
### o. `ps`
Lists your processes
Syntax:
```
```bash
ps -u `yourusername`
```
### p. `kill`
Kills (ends) the processes with the ID you gave
Syntax:
```
```bash
kill `PID`
```
### q. `killall`
Kill all processes with the name
Syntax:
```
```bash
killall `processname`
```
@ -439,28 +451,28 @@ Brings the most recent job in the foreground.
### u. `ping`
Pings host and outputs results
Syntax:
```
```bash
ping `host`
```
### v. `whois`
Gets whois information for domain
Syntax:
```
```bash
whois `domain`
```
### w. `dig`
Gets DNS information for domain
Syntax:
```
```bash
dig `domain`
```
### x. `wget`
Downloads file
Syntax:
```
```bash
wget `file`
```
@ -474,21 +486,21 @@ Now lets discuss about some basic of shell programming. Lets start with creating
Creating variable in bash is similar to other language. There are no data types. A variable in bash can contain a number, a character, a string of characters. You have no need to declare a variable, just assigning a value to its reference will create it.
Example:
```
```bash
str="hello world"
```
The above line creates a variable `str` and assigns "hello world" to it. Then the value of variable is retrieved by putting the `$` in the beginning of variable name.
Example:
```
```bash
echo $str # hello world
```
Also like other languages bash has also arrays. An array is variable containing multiple values. There's no maximum limit on the size of array. Array in bash are zero based. The first element is indexed with element 0. There are several ways for creating arrays in bash. Which are given below.
Examples:
```
```bash
array[0] = val
array[1] = val
array[2] = val
@ -497,19 +509,19 @@ array(val val val)
```
To display a value at specific index use following syntax
```
```bash
${array[i]} # where i is the index
```
One thing to note that if no index is supplied, array element 0 is assumed. To find out how many values there are in the array check following syntax
```
```bash
${#array[@]}
```
Bash has also support for the ternary conditions. Check some examples below.
```
```bash
${varname:-word} # if varname exists and isn't null, return its value; otherwise return word
${varname:=word} # if varname exists and isn't null, return its value; otherwise set it word and then return its value
${varname:+word} # if varname exists and isn't null, return word; otherwise return null
@ -520,7 +532,7 @@ ${varname:offset:length} # performs substring expansion. It returns the subst
Check some of the syntax on how to manipulate strings
```
```bash
${variable#pattern} # if the pattern matches the beginning of the variable's value, delete the shortest part that matches and return the rest
${variable##pattern} # if the pattern matches the beginning of the variable's value, delete the longest part that matches and return the rest
${variable%pattern} # if the pattern matches the end of the variable's value, delete the shortest part that matches and return the rest
@ -534,14 +546,14 @@ ${#varname} # returns the length of the value of the variable as a character
As in almost any programming language, you can use functions to group pieces of code in a more logical way or practice the divine art of recursion. Declaring a function is just a matter of writing function my_func { my_code }. Calling a function is just like calling another program, you just write its name.
Syntax:
```
```bash
functname() {
shell commands
}
```
Example:
```
```bash
#!/bin/bash
function hello {
echo world!
@ -561,7 +573,7 @@ When you will run above example the `hello` function will output "world!". The a
The conditional statement in bash is similar to other programming languages. Conditions have many form like the most basic form is `if` expression `then` statement where statement is only executed if expression is true.
Syntax:
```
```bash
if [expression]; then
will execute only if expression is true
else
@ -572,7 +584,7 @@ fi
Sometime if conditions becoming confusing so you can write the same condition using the `case statements`.
Syntax:
```
```bash
case expression in
pattern1 )
statements ;;
@ -584,7 +596,7 @@ esac
Expression Examples:
```
```bash
statement1 && statement2 # both statements are true
statement1 || statement2 # one of the statement is true
@ -623,7 +635,7 @@ file1 -ot file2 # file1 is older than file2
There are three types of loops in bash. `for`, `while` and `until`.
Different `for` Syntax:
```
```bash
for x := 1 to 10 do
begin
statements
@ -641,14 +653,14 @@ done
```
`while` Syntax:
```
```bash
while condition; do
statements
done
```
`until` Syntax:
```
```bash
until condition; do
statements
done
@ -684,7 +696,7 @@ cd hotellogs
You can easily debug the bash script by passing different options to `bash` command. For example `-n` will not run commands and check for syntax errors only. `-v` echo commands before running them. `-x` echo commands after command-line processing.
Syntax:
```
```bash
bash -n scriptname
bash -v scriptname
bash -x scriptname