Bash

Functions Info

apropos - List of man pages for possible matches based on a search term.

Commands

Man Page Organization

Man Page
Redirecting Standard Output
.bash
```
ls -l /usr/bin > ls-output.txt
```
- This makes output of ls command
About uniq
- uniq to remove any duplicates from the output of the sort command.
  .bash
```
ls /bin /usr/bin | sort | uniq
```
- To see the list of duplicates instead, add the d option to uniq
  .bash
```
ls /bin /usr/bin | sort | uniq -d
```
About tee
- tee is like ls > output.txt but it can work with grep command.
  .bash
```
ls /usr/bin | tee ls.txt | grep zip
```
About echo
.bash
```
echo $((2 + 2))
```
Symbols

Symbols
echo Arithmetic Exponentiation can be nested
.bash
```
echo $(($((5**2)) * 3))
```
The range of integers.
.bash
```
echo {1..10}
echo a{A{1,2},B{3,4}}b
```
Enverment Value List
.bash
```
cli printenv | less
set | less
```

History

To see the history
.bash
```
history
```
History Command

History Command
History Expansion Commands

History Expansion Commands
To record the command
.bash
```
script
```

Permissions

To see the group number
.bash
```
id
```
File Type

File Type
Permission Attributes -rwxrwxr–

Permission Attributes -rwxrwxr–
File Modes in Binary and Octal

File Modes in Binary and Octal
The attribute for changing the file permission
- 7 (rwx), 6 (rw-), 5 (r-x), 4 (r--), and 0 (---)
chmod Symbolic Notation

chmod Symbolic Notation

chmod Symbolic Notation Examples
umask command controls the default permissions given to a file when it is created.
.bash
```
umask 005
```

File System

Testing and Repairing File Systems
.bash
```
sudo fsck /dev/sdb1
```
Make bootable USB drive
.bash
```
sudo dd bs=4M if=path/to/input.iso of=/dev/sd<?> conv=fdatasync  status=progress
```

Helpful Command

Execute find file with command use xargs
.bash
```
find ~ -type f -name "index.html" | xargs ls -l
```
Use find to find the file
.bash
```
find ~ -type f -name "index.html"
```
Best way to compress in tar
.bash
```
tar cfJ playground.tar.xz playground
```
How to Mount ISO File on Linux
.bash
```
mount -t iso9660 -o loop image.iso /mnt/iso_image
```
How to sort in Linux
.bash
```
sort -nk 5

# With command

ls -l /usr/share | sort -nk 5

# Sort in ':'

sort -ht ':' -k 3 /etc/passwd | head
```
Remove Duplicate use uniq
.bash
```
sort foo.txt | uniq
```
Spell check in Terminal
.bash
```
aspell check filename

# To check HTML code

aspell -H check html-filename
```
To make PDF
.bash
```
ls -l ~/ | pr pr.ps | groff > pr.ps

# Convert PostScript file into Potable Document File

ps2pdf pr.ps pr.pdf
```
Good Locations for Scripts
- ~/binScripts intended for personal use.
- /usr/local/binScript that everyone on a system is allowed to use.
- /usr/local/sbinScripts intended for use by the system administrator
- /usr/localLocally supplied software, scripts and compiled programs

Shell Script

Assigning Values to Variables and Constants.
.bash
```
a=z # Assign the string "z" to variable a.
b="a string" # Embedded spaces must be within quotes.
c="a string and $b" # Other expansions such as variables can be expanded into the assignment.
d="$(ls -l foo.txt)" # Results of a command.
e=$((5 * 7)) # Arithmetic expansion.
f="\t\ta string\n" # Escape sequences such as tabs and newlines.
```
Using variables with other commands.
.bash
```
filename="myFile"
touch file
mv file ${filename}
```
Shell Functions
.bash
```
# !/bin/bash

z=human # Gobal variable

echo_1() {
echo "hello"
return
}

echo_2() {
i=world # local veariable
echo "world"
return
}

echo ${echo_1} ${echo_2} $z
```
Flow Control: Branching with if
- if
  .bash
```
x=5
if [ "$x" -eq 5 ]; then
echo "x equals 5."
else
echo "x does not equal 5."
fi
```
- if in shell
  .bash
```
if [ “$x” -eq 5 ]; then echo "equals 5"; else echo "does not equal 5"; fi
```
- if, elif and else
  .bash
```
if commands; then
commands
[elif commands; then
commands...]
[else
commands]
fi
```

Expressions Examples

File Expressions
.bash
```
#!/bin/bash
# test-file: Evaluate the status of a file
FILE=~/.bashrc
if [ -e "$FILE" ]; then
if [ -f "$FILE" ]; then
echo "$FILE is a regular file."
fi
if [ -d "$FILE" ]; then
echo "$FILE is a directory."
fi
if [ -r "$FILE" ]; then
echo "$FILE is readable."
fi
if [ -w "$FILE" ]; then
echo "$FILE is writable."
fi
if [ -x "$FILE" ]; then
echo "$FILE is executable/searchable."
fi
else
echo "$FILE does not exist"
exit 1
fi
exit
```
String Expressions
.bash
```
#!/bin/bash
# test-string: evaluate the value of a string
ANSWER=maybe
if [ -z "$ANSWER" ]; then
echo "There is no answer." >&2
exit 1
fi
if [ "$ANSWER" = "yes" ]; then
echo "The answer is YES."
elif [ "$ANSWER" = "no" ]; then
echo "The answer is NO."
elif [ "$ANSWER" = "maybe" ]; then
echo "The answer is MAYBE."
else
echo "The answer is UNKNOWN."
fi
```
Integer Expressions
.bash
```
#!/bin/bash
# test-integer: evaluate the value of an integer.
INT=-5
if [ -z "$INT" ]; then
echo "INT is empty." >&2
exit 1
fi
if [ "$INT" -eq 0 ]; then
echo "INT is zero."
else
if [ "$INT" -lt 0 ]; then
echo "INT is negative."
else
echo "INT is positive."
fi
if [ $((INT % 2)) -eq 0 ]; then
echo "INT is even."
else
echo "INT is odd."
fi
fi
```
File Expressions

| Expression | Is True If: |

| --- | --- |
| file1 -ef file2 | file1 and file2 have the same inode numbers (the two filenames refer to the same file by hard linking). |
| file1 -nt file2 | file1 is newer than file2. |
| file1 -ot file2 | file1 is older than file2. |
| -b file | file exists and is a block-special (device) file. |
| -c file | file exists and is a character-special (device) file. |
| -d file | file exists and is a directory. |
| -e file | file exists. |
| -f file | file exists and is a regular file. |
| -g file | file exists and is set-group-ID. |
| -G file | file exists and is owned by the effective group ID. |
| -k file | file exists and has its “sticky bit” set. |
| -L file | file exists and is a symbolic link. |
| -O file | file exists and is owned by the effective user ID. |
| -p file | file exists and is a named pipe. |
| -r file | file exists and is readable (has readable permission for the effective user). |
| -s file | file exists and has a length greater than zero. |
| -S file | file exists and is a network socket. |
| -t fd | fd is a file descriptor directed to/from the terminal. This can be used to determine whether standard input/output/error is being redirected. |
| -u file | file exists and is setuid. |
| -w file | file exists and is writable (has write permission for the effective user). |
| -x file | file exists and is executable (has execute/search permission for the effective user). |

String Expressions

| Expression | Is True If… |

| --- | --- |
| string | string is not null. |
| -n string | The length of string is greater than zero. |
| -z string | The length of string is zero. |
| `string1 = string2` `string1 == string2` | string1 and string2 are equal. Single or double equal signs may be used. The use of double equal signs is supported by bash and is generally preferred, but it is not POSIX compliant. |
| string1 != string2 | string1 and string2 are not equal. |
| string1 > string2 | string1 sorts after string2. |
| string1 < string2 | string1 sorts before string2. |

Integer Expressions

Expression	Is True If…
integer1 -eq integer2	integer1 is equal to integer2.
integer1 -ne integer2	integer1 is not equal to integer2.
integer1 -le integer2	integer1 is less than or equal to integer2.
integer1 is less than or equal to integer2.	integer1 is less than integer2.
integer1 -ge integer2	integer1 is greater than or equal to integer2.
integer1 -gt integer2	integer1 is greater than integer2.

AK#Notes

Bash

Commands

About `echo`

History

Permissions

File System

Helpful Command

Shell Script

Expressions Examples

Bash

Commands

About echo

History

Permissions

File System

Helpful Command

Shell Script

Expressions Examples

About `echo`