Linux Useful utils
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Which Shell are you running?
- Execute the command
echo $0
- Execute the command
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Aborting and suspending the execution of linux programs
- Control-Z suspends the program
- Control-C aborts the program
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Redirecting output of a command to a file instead of terminal (stdout)
command > file
- Eg: ping -c 4 google.com > pingresults.txt
- If you want to append the text to existing file use >>
- Eg: ping -c 10 google.com >> pingresults.txt
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Redirecting input can be done using < eg: head < /proc/cpuinfo
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Common Errors
- NO Such file or directory
- file exists
- Not a Directory, Is a directory
- NO space left of device
- Permission Denied
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What is softlink (symbolic link) in linux and what is hardlink?
- Softlink(symbolic) is an actual link to original file whereas hard link is a mirror copy of original file.
- If you delete the original file, soft link has no value (since t whatever file it points no longer exists)
- If you delete the original file, hard link will still has the data of the original file
- Softlink
- Can cross the file systems
- Allows yo to link between directories
- permissions will not be updated
- has only the path to original file not contents
- Hard link
- Can’t cross file system boundaries (it exist on same filesystem)
- can’t link directories
- permissions will be updated if we change the source
- It has contents of original file
- Create a Symlink or softlink
- Create a hardlink
- What will be difference between hard link and normally copied file?
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Identifying Commands
- type: Type is a shell builtin command which displays the kind of command once you give a particular command
type ls type cp type ping type type
- which-Display an Executable location
which ls
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Getting a Commands Documentation
- help: bash has a built-in help facility for each of the shell builtins.
help cd
- –help: Many executable programs support a –help option displays the description of commands
mkdir --help
- man: Most executable programs intended for command line usage will provide manual
man <command> man ls
- apropos-Display appropriate commands
apropos partition
- info command: This commadn will show mauals with hyperlinked much like web docs
Pipelines
- Is a capability of commands to read output of command as input to other command
- Generally operator | is referred as pipe
command1 | command2
- Pipelines are often used to perform complex operations on data. It is possible for you to put several commands together into a pipeline
ls -al /bin /usr/bin | sort | less
ls -al /bin /usr/bin/ | sort | uniq | wc -l
tee
- tee command will read from stdin and send the output to stdout and files
ls -al /bin /usr/bin | tee ls.txt | sort | uniq | wc -l