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70 Cards in this Set
- Front
- Back
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What is the difference between ‘single quotes’ and “double quotes”? |
‘single quotes’ are strong quotes and will not allow expansion of variables.“double quotes” are weak quotes and will allow expansion of variables.Ex: If you have a variable var=123echo ‘$var’ will not return the value of that variable.echo “$var” will return the value of that variable (123). |
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Command: ^s |
What it does: halt output to screen |
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Command: ^d |
What it does: end of input |
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Command:^c |
What it does: stop current command |
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Command:^q |
What it does: restart output to screen |
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Command:^/ |
What it does: stop current command |
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Wildcard: ? |
any single character |
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Wildcard: * |
any string of characters |
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Wildcard: [set] |
any character in set |
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Wildcard: [!set] |
any character not in set |
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What is PATH? |
An environmental variable that tells SHELL which directory to search for exe files |
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Describe what #! does. (known as interpreter) |
The shebang is a directive to the loader to use the program that’s specified after it and tells Linux what program to run |
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/bin |
binaries (executables) |
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/sbin |
System binaries |
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/libexec |
/lib/ is essential shared libraries, /libexec is for binary system executables |
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/etc |
System configuration |
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/var |
variables (logs, files that support services/programs) |
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/tmp |
temporary |
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Command |
What it does? |
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which |
path a utility is located |
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ls |
list all files and directories except hidden ones |
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echo |
prints to stdout |
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man |
manual pages |
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cd |
change directory |
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cat |
prints to stdout |
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whereis |
Locates binary, source, and manual pages for a file |
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touch |
create file, if file exist then it will update the timestamps |
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umask |
Masks the permissions, takes them away |
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chmod |
change permission of file or directory |
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mkdir |
create directory |
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rmdir |
remove directory |
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rm |
remove file |
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test |
check file types and compare values |
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export |
Creative environmental variables |
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read |
input from stdin |
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builtin |
test if it is built in command |
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test -e “filename” |
check if the file exists |
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test -f “filename” |
checks if the file is the regular file |
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test -d “filename” |
checks if the file is a directory |
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test -c “filename” |
checks if the file exists and is character special |
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test -b “filename” |
checks if the file exists and is block special |
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test -r “filename” |
checks if the file is readable |
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test -w “filename” |
checks if the file can be written by the user |
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test -x “filename” |
checks if the file can be executed |
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test -z “filename” |
checks if the length of string is zero |
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test -n “filename” |
checks if the length of string is nonzero |
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ls -a |
list all files including hidden |
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ls -l |
display result in long format |
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ls -d |
use in conjunction with the -l option to see details about the dir rather than its contents |
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ls -r |
display results in reverse order |
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ls -S |
sort results by file size |
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ls -t |
sort by modification time |
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ls -n |
sort by numerical order |
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echo $? |
checks if the command ran properly |
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What is piping? |
output of 1st command is inputted into 2nd command |
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What is the difference between curly brackets { }, square brackets [ ] , parentheses ( ) , and double parentheses (( )) |
curly brackets { } string extension square brackets [ ] conditional string parentheses ( ) used for subshells double parentheses (( )) for integer expression |
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-eq |
equal |
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-ne |
not equal |
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-lt |
less than |
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-le |
less than or equal |
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-gt |
greater than |
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-ge |
greater than or equal |
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${varname:-word} |
If varname exists and isn’t null, return its value; otherwise return word |
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${varname:=word} |
If varname exists and isn’t null, return its value; otherwise set it to word and then return it’s value |
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${varname:?message} |
If varname exists and isn’t null, return its value; otherwise print varname; followed by message, and abort current command or script |
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${varname:offset:length} |
Performs substring expansion. It returns the substring of $varname starting at offset and up to length characters. The first character in $varname is position 0 |
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${varname#pattern} |
If the pattern matches the beginning of the variable’s value, delete the shortest part that matches and return the rest |
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${varname##pattern} |
If the pattern matches the beginning of the variable’s value, delete the longest part that matches and return the rest |
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${varname%pattern} |
If the pattern matches the end of the variable’s value, delete the shortest part that matches and return the rest |
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${varname%%pattern} |
If the pattern matches the end of the variable’s value, delete the longest part that matches and return the rest |
