Bash Scripting

‘\r’: command not found - .bashrc / .bash_profile [duplicate]

When all else fails in Cygwin…

Try running the dos2unix command on the file in question.

It might help when you see error messages like this:

-bash: '\r': command not found

Windows style newline characters can cause issues in Cygwin.

The dos2unix command modifies newline characters so they are Unix / Cygwin compatible.

CAUTION: the dos2unix command modifies files in place, so take precaution if necessary.

If you need to keep the original file, you should back it up first.

Note for Mac users: The dos2unix command does not exist on Mac OS X.

Check out this answer for a variety of solutions using different tools.

There is also a unix2dos command that does the reverse:

It modifies Unix newline characters so they’re compatible with Windows tools.

If you open a file with Notepad and all the lines run together, try unix2dos filename.

Source: ‘\r’: command not found - .bashrc / .bash_profile [duplicate]

How To Set Environment Variable in Bash

export VAR="my value"

echo $VAR
printenv VAR

Source: How To Set Environment Variable in Bash

Index a String in bash

${string:position}

Extracts substring from $string at $position.

If the $string parameter is “*” or “@”, then this extracts the positional parameters, starting at $position.

${string:position:length} Extracts $length characters of substring from $string at $position.

Source: Index a String in bash

Extract substring in Bash

You can use Parameter Expansion to do this.

If a is constant, the following parameter expansion performs substring extraction:

b=${a:12:5}

echo that outputs to stderr

>&2 echo "error"

Source: echo that outputs to stderr

Linux bash exit status and how to set exit status in bash

Exit Code	Description
0	Success
1	Operation not permitted
2	No such file or directory
3	No such process
4	Interrupted system call
5	Input/output error
6	No such device or address
7	Argument list too long
8	Exec format error
9	Bad file descriptor
10	No child processes
11	Resource temporarily unavailable
12	Cannot allocate memory
13	Permission denied
14	Bad address
15	Block device required
16	Device or resource busy
17	File exists
18	Invalid cross-device link
19	No such device
20	Not a directory
21	Is a directory
22	Invalid argument
23	Too many open files in system
24	Too many open files
25	Inappropriate ioctl for device
26	Text file busy
27	File too large
28	No space left on device
29	Illegal seek
30	Read-only file system
31	Too many links
32	Broken pipe
33	Numerical argument out of domain
34	Numerical result out of range
35	Resource deadlock avoided
36	File name too long
37	No locks available
38	Function not implemented
39	Directory not empty
40	Too many levels of symbolic links
42	No message of desired type
43	Identifier removed
44	Channel number out of range
45	Level 2 not synchronized
46	Level 3 halted
47	Level 3 reset
48	Link number out of range
49	Protocol driver not attached
50	No CSI structure available
51	Level 2 halted
52	Invalid exchange
53	Invalid request descriptor
54	Exchange full
55	No anode
56	Invalid request code
57	Invalid slot
59	Bad font file format
60	Device not a stream
61	No data available
62	Timer expired
63	Out of streams resources
64	Machine is not on the network
65	Package not installed
66	Object is remote
67	Link has been severed
68	Advertise error
69	Srmount error
70	Communication error on send
71	Protocol error
72	Multihop attempted
73	RFS specific error
74	Bad message
75	Value too large for defined data type
76	Name not unique on network
77	File descriptor in bad state
78	Remote address changed
79	Can not access a needed shared library
80	Accessing a corrupted shared library
81	.lib section in a.out corrupted
82	Attempting to link in too many shared libraries
83	Cannot exec a shared library directly
84	Invalid or incomplete multibyte or wide character
85	Interrupted system call should be restarted
86	Streams pipe error
87	Too many users
88	Socket operation on non-socket
89	Destination address required
90	Message too long
91	Protocol wrong type for socket
92	Protocol not available
93	Protocol not supported
94	Socket type not supported
95	Operation not supported
96	Protocol family not supported
97	Address family not supported by protocol
98	Address already in use
99	Cannot assign requested address
100	Network is down
101	Network is unreachable
102	Network dropped connection on reset
103	Software caused connection abort
104	Connection reset by peer
105	No buffer space available
106	Transport endpoint is already connected
107	Transport endpoint is not connected
108	Cannot send after transport endpoint shutdown
109	Too many references
110	Connection timed out
111	Connection refused
112	Host is down
113	No route to host
114	Operation already in progress
115	Operation now in progress
116	Stale file handle
117	Structure needs cleaning
118	Not a XENIX named type file
119	No XENIX semaphores available
120	Is a named type file
121	Remote I/O error
122	Disk quota exceeded
123	No medium found
125	Operation canceled
126	Required key not available
127	Key has expired
128	Key has been revoked
129	Key was rejected by service
130	Owner died
131	State not recoverable
132	Operation not possible due to RF-kill
133	Memory page has hardware error

Source: Linux bash exit status and how to set exit status in bash

Shell Script : How to check if variable is null or no

if [[ "$is_always_execute" == null ]];
then
    is_always_execute=false;
fi

if [[ -n "$list_Data" ]]
then
    echo "not Empty"
else
    echo "empty"
fi

if [[ -z "$list_Data" ]]
then
  echo "Empty"
else
  echo "Not empty"
fi

Source: Shell Script : How to check if variable is null or no

While loop

while [ condition ]
do
   command1
   command2
   command3
done

Source: Bash While Loop Examples

Sleep

sleep <n_SECONDS>

eg. sleep 1 - sleep for 1 second

Compare Strings in Bash

Example-1: String Comparison using “==” operators

#!/bin/bash

strval1="Ubuntu"
strval2="Windows"

#Check equality two string variables

if [ $strval1 == $strval2 ]; then
  echo "Strings are equal"
else
  echo "Strings are not equal"
fi

#Check equality of a variable with a string value

if [ $strval1 == "Ubuntu" ]; then
  echo "Linux operating system"
else
  echo "Windows operating system"
fi

Example-2: String Comparison using “!=” operator

#!/bin/bash

strval1="Ubuntu"
strval2="Windows"

#Check inequality of a variable with a string value

if [ $strval2 != "Ubuntu" ]; then
  echo "Windows operating system"
else
  echo "Linux operating system"
fi

Example-3: Partial String Comparison

#!/bin/bash

strval="Microsoft Internet Explorer"

if [[ $strval == *Internet* ]];
then
  echo "Partially Match"
else
  echo "No Match"
fi

if [[ $strval == *internet* ]];
then
  echo "Partially Match"
else
  echo "No Match"
fi

Example-4: Compare string with user input value

#!/bin/bash

echo "Enter Your Name"
read input

if [ $input != "Fahmida" ];
then
  echo "No Record Found"
else
  echo "Record Found"
fi

Source: How to compare strings in Bash

Create a bash script

Place a shebang at the top of the script

#!/bin/bash

Running a bash script

Use:

bash scriptname.sh

instead of:

sh scriptname.sh

if..else Statement

if statement

if TEST-COMMAND
then
  STATEMENTS
fi

if else statement

if TEST-COMMAND
then
  STATEMENTS1
else
  STATEMENTS2
fi

if..elif..else

if TEST-COMMAND1
then
  STATEMENTS1
elif TEST-COMMAND2
then
  STATEMENTS2
else
  STATEMENTS3
fi

nested if

#!/bin/bash

echo -n "Enter the first number: "
read VAR1
echo -n "Enter the second number: "
read VAR2
echo -n "Enter the third number: "
read VAR3

if [[ $VAR1 -ge $VAR2 ]]
then
  if [[ $VAR1 -ge $VAR3 ]]
  then
    echo "$VAR1 is the largest number."
  else
    echo "$VAR3 is the largest number."
  fi
else
  if [[ $VAR2 -ge $VAR3 ]]
  then
    echo "$VAR2 is the largest number."
  else
    echo "$VAR3 is the largest number."
  fi
fi

multiple conditions

#!/bin/bash

echo -n "Enter the first number: "
read VAR1
echo -n "Enter the second number: "
read VAR2
echo -n "Enter the third number: "
read VAR3

if [[ $VAR1 -ge $VAR2 ]] && [[ $VAR1 -ge $VAR3 ]]
then
  echo "$VAR1 is the largest number."
elif [[ $VAR2 -ge $VAR1 ]] && [[ $VAR2 -ge $VAR3 ]]
then
  echo "$VAR2 is the largest number."
else
  echo "$VAR3 is the largest number."
fi

Below are some of the most commonly used operators:

• -n VAR - True if the length of VAR is greater than zero.
• -z VAR - True if the VAR is empty.
• STRING1 = STRING2 - True if STRING1 and STRING2 are equal.
• STRING1 != STRING2 - True if STRING1 and STRING2 are not equal.
• INTEGER1 -eq INTEGER2 - True if INTEGER1 and INTEGER2 are equal.
• INTEGER1 -gt INTEGER2 - True if INTEGER1 is greater than INTEGER2.
• INTEGER1 -lt INTEGER2 - True if INTEGER1 is less than INTEGER2.
• INTEGER1 -ge INTEGER2 - True if INTEGER1 is equal or greater than INTEGER2.
• INTEGER1 -le INTEGER2 - True if INTEGER1 is equal or less than INTEGER2.
• -h FILE - True if the FILE exists and is a symbolic link.
• -r FILE - True if the FILE exists and is readable.
• -w FILE - True if the FILE exists and is writable.
• -x FILE - True if the FILE exists and is executable.
• -d FILE - True if the FILE exists and is a directory.
• -e FILE - True if the FILE exists and is a file, regardless of type (node, directory, socket, etc.).
• -f FILE - True if the FILE exists and is a regular file (not a directory or device).

Source: Bash if..else Statement

How to Evaluate Strings as Numbers in Bash

To convert strings to integers in bash, wrap them in $((X)). Like this:

$((string))

What is .bashrc file in Linux?

Source: https://www.digitalocean.com/community/tutorials/bashrc-file-in-linux

How to Create and Use Alias Command in Linux

alias shortName="your custom command here"

Creating Permanent Aliases

vim ~/.bashrc
#My custom aliases
alias home=”ssh -i ~/.ssh/mykep.pem tecmint@192.168.0.100”
alias ll="ls -alF"

source ~/.bashrc

Source: https://www.tecmint.com/create-alias-in-linux/

The set builtin

• https://www.gnu.org/software/bash/manual/html_node/The-Set-Builtin.html

bash : Bad Substitution

Make sure your script didnt have

#!/bin/sh

at the top of your script. Instead, you should add

#!/bin/bash

https://stackoverflow.com/questions/20615217/bash-bad-substitution

Understanding Exit Codes and Using them in Bash scripts

• https://madflojo.medium.com/understanding-exit-codes-in-bash-6942a8b96ce5