BasicLinuxComands.md

Basic Commands in Linux & Git

• cat filename : shows contents of file
• more filename: shows contents of file
• less filename: shows contents but removes all other terminal objs, exit with q
• cat > filename: creates file
• touch filename: generates new or updates time stamp on existing file
• cat filename1 filename2 > otherfile: in order writes/overwrites file 1 & 2 onto other file
  • IF cat file3 > otherfile is ran after the previous command it will overwrite otherfile with file 3 contents
• cat filename1 >> otherfile: keeps the contents of otherfile and appends it with file 1 contents
• -r: gives acces to modify directories
• wc filename: gives (# of lines, # of words, # of characters)
  • wc -l: gives line count

Removal

• rm -rf: rm is remove -r recursive i.e. remove all sub dir, f force

Error Messages

• live in the channel called Standard Error stderr
• using 2>, 2>> makes it so the standard message, which might be a blank overwriting of a file bc the first file DNE instead will write the erro into the file so you're aware that an error occurred.
• Actually I have no idea
  • cat filename1 2>> otherfile: seems to only show file 1 contents on terminal but not overwrite/append otherfile.
  • IF cat filethatdoesnotexists 2>> otherfile is used it will append otherfile and say the file DNE
  • IF cat filethatdoesnotexists 2> otherfile is used it will overwrite the file and say it DNE
• redirect input into an output file
  • e.g wc -l < filename1 >> output_wordcount.txt
    • this takes the command word count and applies it to file 1 then takes that output #number of lines and appends it to the output txt file.
• sort filename: sorts the lines of the file by number then by letter (IMPORTANT IT'S BY CHARACTER)
• head -number or tail -number: can take the 1st or last lines

Redirect ALL standard error

• use &>: can capture standard AND stderr in a file
  • Most useful
  • e.g.:
    • ls &> filename1 : writes the ls files to a file
    • cat filename1: check the contents
    • ls filethatDNE &> filename1
    • cat filename: rewritten error message

Create multiple directories at once

• touch dir1/dir2/newdir{,1,2}
  • this will create within dir2: newdir, newdir1, newdir2

Conditional Commands

• &&: runs the second command only if the first one succeeds
  • e.g.:
    • cd into a dir and rm all contents in final dir
    • cd dir1/dir2 && rm*
• ||: runs the second only if the first fails
• ;: lets you put multiple commands all on one line running unconditionally - runs all at the same time

Putting the error messages in a file

• Maybe you don't want the error messages to populate in your file
• we can create a err.log file and pipe the error into it as we try to make changes
• e.g.:
  • cat filethatdoesnotexists >> output.txt 2>> err.log
  • the error message is now in the log and not in the desired file

Find

• find: searches any dir and sub dir
  • find . -name file.txt

Grep (also finding)

• Search the contents of any file
• grep word *.txt: find all .txt files that contain the word "word"
• grep -i WorD *.txt: find all with out the case sensitivity
• grep -in WorD *.txt: find the file and show the line it is found in
• grep -il WorD *.txt: gives all the files that contain the word
• grep -rli WorD .: find all case insensitive instances within all subdirectories
• Search Recursively:
  • greop -rli aPPle .
• which
  • e.g.:which ls : tells about ls
• whereis
  • e.g.: whereis ls : tells where the file is

Wildcard *, ?, []

• all used for pattern matching aka "globbing"
• e.g.: ls *.txt
  • shows all txt files
• ?: matches characters
  • e.g.:
    • ls *.??
    • show all files with only two end characters,as in
      • .md, .sh, .ex...
• [] shows a range of characters
  • e.g.: ls [e-f]*
    • shows any file that starts with e or f
  • e.g.: ls [e-f]*.txt
    • same but we want them to be text files only

Accessing Bash to create alias

• commands:
  • cd
  • ls - a
  • find .bashrc and open to edit
  • add alias and restart terminal

Git

• git status -s: shortened version of status, of untracked or tracked changes
• git log --oneline
  • git checkout ID230482 ID found from prev. command -able to look around
  • git checkout main return to future
• git checkout -- filename : if you did not like the changes you made to this particular file this command will return it to the most recent saved version !

Fortran