Bash script notable cheat-sheet

1.if-statements-operator.md

Operator	Description
! EXPRESSION	The EXPRESSION is false.
condition 1 -a condition 2	CONDITION 1 and CONDITION 2.
condition 1 -o condition 2	CONDITION 1 or CONDITION 2.
-n STRING	The length of STRING is greater than zero.
-z STRING	lengh of STRING is zero (ie it is empty).
STRING1 =/!= STRING2	STRING1 is equal/not-equal to STRING2
INTEGER1 -eq/ne INTEGER2	INTEGER1 is numerically equal/not-equal to INTEGER2
INTEGER1 -gt/lt INTEGER2	INTEGER1 is numerically greater than or less than INTEGER2
INTEGER1 -ge/le INTEGER2	INTEGER1 is numerically greater-than/less-than or equal to INTEGER2
-b/c FILE	FILE is a block/character device.
-d/f/p/S FILE	FILE exists and is a directory/regular-file/pipe/socket.
-e FILE	FILE exists.
-h/L FILE	FILE is a symbolic link.
-s FILE	FILE exists and it's SIZE is greater than ZERO (ie. it is not empty).
-r/w/x FILE	FILE exists and read/write/execute permission is granted.
f1 -nt/ot/ef f2	FILE 1 is newer-than/older-than/has-hard-link-to-same-file

Source: Bash Script Tutorial - 5. If Statements & File test operators

2.special-variables.md

Symbol	Meaning
$0	The name of the Bash script.
$1-$9	The first 9 arguments to the Bash script. (As mentioned above.)
$#	How many arguments were passed to the Bash script.
$@	All the arguments supplied to the Bash script.
$?	The exit status of the most recently run process.
$$	The process ID of the current script.
$USER	The username of the user running the script.
$HOSTNAME	The hostname of the machine the script is running on.
$SECONDS	The number of seconds since the script was started.
$RANDOM	Returns a different random number each time is it referred to.
$LINENO	Returns the current line number in the Bash script.

Source: Bash Scripting Tutorial - 2. Variables

3.exit-status.md

Exit Status Code	Description
0	success
1	failure, as defined by the program
2	command line usage error
different value than those above	custom exit code for specific program

4.error-codes.md

Bash exit codes

Exit Code Number	Meaning	Examples	Comments
1	Catchall for general errors	let "var1 = 1/0"	Miscellaneous errors, such as "divide by zero" and other impermissible operations
2	Misuse of shell builtins		Missing keyword or command, or permission problem (and diff return code on a failed binary file comparison)
124	You need to be root		System script started as a non-root user
125	Unconfigured		Missing configuration file or value
126	Command invoked cannot execute		Permission problem or command is not an executable
127	"command not found"		Possible problem with $PATH or a typo
128	Invalid argument to exit	exit 3.14159	exit takes only integer args in the range 0 - 255
128+n	Fatal error signal "n"	kill -9 $PPIDof script	$? returns 137 (128 + 9)
130	Script terminated by Control-C	Control-C is fatal error signal 2, (130 = 128 + 2, see above)
255	Exit status out of range	exit -1	exit takes only integer args in the range 0 - 255

Github source: debian-server-tools

Source: Advanced Bash-Scripting Guide Appendix E. & Appendix C. Exit Codes With Special Meanings

Custom Exit Code Numbers are marked in italic.

5.error-numbers&codes.md

Error No.	Error Name	Error description
1	EPERM	Operation not permitted
2	ENOENT	No such file or directory
3	ESRCH	No such process
4	EINTR	Interrupted system call
5	EIO	/O error
6	ENXIO	No such device or address
7	E2BIG	Arg list too long
8	ENOEXEC	Exec format error
9	EBADF	Bad file number
10	ECHILD	No child processes
11	EAGAIN	Try again
12	ENOMEM	Out of memory
13	EACCES	Permission denied
14	EFAULT	Bad address
15	ENOTBLK	Block device required
16	EBUSY	Device or resource busy
17	EEXIST	File exists
18	EXDEV	Cross-device link
19	ENODEV	No such device
20	ENOTDIR	Not a directory
21	EISDIR	Is a directory
22	EINVAL	Invalid argument
23	ENFILE	File table overflow
24	EMFILE	Too many open files
25	ENOTTY	Not a typewriter
26	ETXTBSY	Text file busy
27	EFBIG	File too large
28	ENOSPC	No space left on device
29	ESPIPE	Illegal seek
30	EROFS	Read-only file system
31	EMLINK	Too many links
32	EPIPE	Broken pipe
33	EDOM	Math argument out of domain of func
34	ERANGE	Math result not representable
35	EDEADLK	Resource deadlock would occur
36	ENAMETOOLONG	File name too long
37	ENOLCK	No record locks available
38	ENOSYS	Function not implemented
39	ENOTEMPTY	Directory not empty
40	ELOOP	Too many symbolic links encountered
41	EWOULDBLOCK	Operation would block
42	ENOMSG	No message of desired type
43	EIDRM	Identifier removed
44	ECHRNG	Channel number out of range
45	EL2NSYNC	Level 2 not synchronized
46	EL3HLT	Level 3 halted
47	EL3RST	Level 3 reset
48	ELNRNG	Link number out of range
49	EUNATCH	Protocol driver not attached
50	ENOCSI	No CSI structure available
51	EL2HLT	Level 2 halted
52	EBADE	Invalid exchange
53	EBADR	Invalid request descriptor
54	EXFULL	Exchange full
55	ENOANO	No anode
56	EBADRQC	Invalid request code
57	EBADSLT	Invalid slot
58	EDEADLOCK	File locking deadlock error
59	EBFONT	Bad font file format
60	ENOSTR	Device not a stream
61	ENODATA	No data available
62	ETIME	Timer expired
63	ENOSR	Out of streams resources
64	ENONET	Machine is not on the network
65	ENOPKG	Package not installed
66	EREMOTE	Object is remote
67	ENOLINK	Link has been severed
68	EADV	Advertise error
69	ESRMNT	Srmount error
70	ECOMM	Communication error on send
71	EPROTO	Protocol error
72	EMULTIHOP	Multihop attempted
73	EDOTDOT	RFS specific error
74	EBADMSG	Not a data message
75	EOVERFLOW	Value too large for defined data type
76	ENOTUNIQ	Name not unique on network
77	EBADFD	File descriptor in bad state
78	EREMCHG	Remote address changed
79	ELIBACC	Can not access a needed shared library
80	ELIBBAD	Accessing a corrupted shared library
81	ELIBSCN	.lib section in a.out corrupted
82	ELIBMAX	Attempting to link in too many shared libraries
83	ELIBEXEC	Cannot exec a shared library directly
84	EILSEQ	Illegal byte sequence
85	ERESTART	Interrupted system call should be restarted
86	ESTRPIPE	Streams pipe error
87	EUSERS	Too many users
88	ENOTSOCK	Socket operation on non-socket
89	EDESTADDRREQ	Destination address required
90	EMSGSIZE	Message too long
91	EPROTOTYPE	Protocol wrong type for socket
92	ENOPROTOOPT	Protocol not available
93	EPROTONOSUPPORT	Protocol not supported
94	ESOCKTNOSUPPORT	Socket type not supported
95	EOPNOTSUPP	Operation not supported on transport endpoint
96	EPFNOSUPPORT	Protocol family not supported
97	EAFNOSUPPORT	Address family not supported by protocol
98	EADDRINUSE	Address already in use
99	EADDRNOTAVAIL	Cannot assign requested address
100	ENETDOWN	Network is down
101	ENETUNREACH	Network is unreachable
102	ENETRESET	Network dropped connection because of reset
103	ECONNABORTED	Software caused connection abort
104	ECONNRESET	Connection reset by peer
105	ENOBUFS	No buffer space available
106	EISCONN	Transport endpoint is already connected
107	ENOTCONN	Transport endpoint is not connected
108	ESHUTDOWN	Cannot send after transport endpoint shutdown
109	ETOOMANYREFS	Too many references: cannot splice
110	ETIMEDOUT	Connection timed out
111	ECONNREFUSED	Connection refused
112	EHOSTDOWN	Host is down
113	EHOSTUNREACH	No route to host
114	EALREADY	Operation already in progress
115	EINPROGRESS	Operation now in progress
116	ESTALE	Stale NFS file handle
117	EUCLEAN	Structure needs cleaning
118	ENOTNAM	Not a XENIX named type file
119	ENAVAIL	No XENIX semaphores available
120	EISNAM	Is a named type file
121	EREMOTEIO	emote I/O error

Source: Exit & Error Codes in bash and Linux OS

6.useful-tips.md

Check how many arguments

if [ $# -ne 2 ]; then
    printf "Check 2 arguments"
    return 1
fi

Conver string to array

IFS=" " read -a array <<< "1 2 3 4"

array=($(echo "one,two,three" | tr ',' '\n'))

Trim 2 last string

new_string=${string%??}