References
Bash Comparisons
Numeric Comparisons
| Comparison |
Description |
| n1 -eq n2 |
Check if n1 is equal to n2 |
| n1 -ge n2 |
Check if n1 is greater than or equal to n2 |
| n1 -gt n2 |
Check if n1 is greater than n2 |
| n1 -le n2 |
Check if n1 is less than or equal to n2 |
| n1 -lt n2 |
Check if n1 is less than n2 |
| n1 -ne n2 |
Check if n1 is not equal to n2 |
String Comparisons
| Comparison |
Description |
| str1 = str2 |
Check if str1 is the same as string str2 |
| str1 != str2 |
Check if str1 is not the same as str2 |
| str1 < str2 |
Check if str1 is less than str2 |
| str1 > str2 |
Check if str1 is greater than str2 |
| -n str1 |
Check if str1 has a length greater than zero |
| -z str1 |
Check if str1 has a length of zero |
The test Command File Comparisons
| Comparison |
Description |
| [-d] file |
Check if file exists and is a directory |
| [-e] file |
Checks if file exists |
| [-f] file |
Checks if file exists and is a file |
| [-s] file |
Checks if file exists and is not empty |
| [-r] file |
Checks if file exists and is readable |
| [-w] file |
Checks if file exists and is writable |
| [-x] file |
Checks if file exists and is executable |
| [-O] file |
Checks if file exists and is owned by the current user |
| [-G] file |
Checks if file exists and the default group is the same as the current user |
| file1 -nt file2 |
Checks if file1 is newer than file2 |
| file1 -ot file2 |
Checks if file1 is older than file2 |
lsof
| Column |
Description |
| COMMAND |
The first nine characters of the name of the command in the process |
| PID |
The process ID of the process |
| USER |
The login name of the user who owns the process |
| FD |
The file descriptor number and access type (r - read, w - write, u - read/write) |
| TYPE |
The type of file (CHR - character, BLK - block, DIR - directory, REG - regular file) |
| DEVICE |
The device numbers (major and minor) of the device |
| SIZE |
If available, the size of the file |
| NODE |
The inode number of the local file |
| NAME |
The name of the file |
Example
lsof -a -p $$ -d 0,1,2
-a: means and conditions together
-p: lsof condition over the specific process
-d: select some file descriptor
Redirection
Docs
Note
- &0 is equel to
/proc/slef/fd/0
- &1 is equel to
/proc/slef/fd/1
- &2 is equel to
/proc/slef/fd/2
Shell Status Code Descriptor
| Code |
Description |
| 0 |
Successful completion of the command Create an empty array |
| 1 |
General unknown error |
| 2 |
2 Misuse of shell command |
| 126 |
The command can’t execute |
| 127 |
Command not found |
| 128 |
Invalid exit argument |
| 128+x |
Fatal error with Linux signal x |
| 130 |
Command terminated with Ctl-C |
| 255 |
Exit status out of range |
Array
| syntax |
result |
| arr=() |
Create an empty array |
| arr=(1 2 3) |
Initialize array |
| ${arr[2]} |
Retrieve third element |
| ${arr[@]} |
Retrieve all elements |
| ${!arr[@]} |
Retrieve array indices |
| ${#arr[@]} |
Calculate array size |
| arr[0]=3 |
Overwrite 1st element |
| arr+=(4) |
Append value(s) |
| str=$(ls) |
Save ls output as a string |
| arr=( $(ls) ) |
Save ls output as an array of files |
| ${arr[@]:s:n} |
Retrieve n elements starting at index s |
| {a,b}{+,-} |
Cartesian multiply |
bc
Calculate numbers with bc command with 5 number flot
echo "scale=5; 100/3" | bc
Compare to number with bc
Dollar-sign
| sign |
means |
| $# |
number of input parameters |
| $0 |
return the current code name |
| $1 |
refer to the first input argument |
| $2 |
refer to the second input argument |
| $N |
refer to the nth input argument |
| $? |
return shell status code/exit code |
| $$ |
return shell process id |
| $! |
return the PID of the last background process |
| $- |
return current shell status |
| $_ |
return last argument from last command |
| !$ |
execute last argument from last command |
| $* |
return the input arguments in one line |
| $@ |
return the input arguments line by line |
Function
| definition |
call |
| function myFunc0{ ... } |
myFunc0 |
| myFunc1() |
myFunc1 mehrdad radin leila |
File Descriptor Options
| Option |
Description |
| -a |
Show all objects |
| -f |
Specify a file to read data from |
| -h |
Display a help message for the command |
| -n |
Do nothing, just display what will happen |
| -o |
Specify an output file to redirect all output to |
| -q |
Run in quiet mode |
| -r |
Process directories and files recursively |
| -s |
Run in silent mode |
| -v |
Produce verbose output |
| -y |
Answer yes to all questions |
Print Screen
| syntax |
result |
| str=$'\e[%d;%dHSalam' |
printf $str 5 10 |
| echo $'\e[10;10HSalam' |
print in the row #10 column #10 |
Read
| argument |
result |
| read -s |
does not echo input |
| read -nN |
accepts only N characters of input |
| read -p |
prompt message |
| read -tT |
accepts input for T second |
String
| sign |
mean |
| ${str}ABC |
add ABC to the end of the string |
| ${str/subSTR/} |
remove sub string from main string |
| ${str/old/new} |
substitute new string with old string |
| {str:=sara} |
print the value of str if exists otherwise print sara |
| {str:-sara} |
print the value of str if exists otherwise print sara |
| {str:?sara} |
print the value of str if exists otherwise print sara |
| {#str} |
return the str length |
| ${str%?} |
remove the last character |
| ${str%#} |
remove the first character |
| ${str%A*} |
remove the characters after A |
| ${str%A*C} |
remove A-C from the end of the string |
| ${str%%A*C} |
remove A-C from the beginning of the string |
| {m:0:3} |
slice string |