> For the complete documentation index, see [llms.txt](https://dev117uday.gitbook.io/notes-md/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://dev117uday.gitbook.io/notes-md/linux/linux-commands-part-1-4.md). # Linux Commands Part 1 - 4 Tags: linux-com-book ## Introductory Commands * `#` before terminal means super-user * `date` to print date and time * `Sat Jun 18 12:01:17 AM IST 2022` * `cal` to print calendar * `df` to print disk drive and usage * `free` to print memory * `pwd` print working directory * `Absolute PathName` : begins with root directory and follows the tree branch by branch till the desired folder * `Relative PathName` : starts from the working directory * `cd` to change directory * `cd -` to revert to previous directory * `cd ~username` : to change directory to another user * ls : to list directories * `ls directory_1 directory_2` : to print list or multiple directories ```java ➜ ~ ls programm software programm: azure-dev-hackathon inbox-app configs learning-springboot demo playground software: jetbrains-toolbox tor-browser_en-US ``` * `ls -l` : for more details * `ls -lt` : to list sorted acc. date modifed * `—reverse` : to reverse the sort ![List of options of ls command](https://473782116-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2F-MlTUR0kU-pvc2XyvuDJ%2Fuploads%2Fgit-blob-690ba4d9e87b8035d625318da3bcbcdc5b953fc9%2FUntitled.png?alt=media) Long Listing Details ![details of fields printing long list](https://473782116-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2F-MlTUR0kU-pvc2XyvuDJ%2Fuploads%2Fgit-blob-2c112a0b67e026bbc8c10fde496b75dc8cf14d42%2FUntitled%201.png?alt=media) * `file filename` : to print a brief description of the file’s contents * `less` : to view content of file ## File Structure ![Linux file structure part 1](https://473782116-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2F-MlTUR0kU-pvc2XyvuDJ%2Fuploads%2Fgit-blob-bbd6dda95aafe9fdb3e7e7f4843ef52d368fa3fd%2FUntitled%202.png?alt=media) ![Linux file structure part 2](https://473782116-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2F-MlTUR0kU-pvc2XyvuDJ%2Fuploads%2Fgit-blob-ab7dc68df2abf790b6bbcc29acebb12fa232c38d%2FUntitled%203.png?alt=media) ![Linux file structure part 3](https://473782116-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2F-MlTUR0kU-pvc2XyvuDJ%2Fuploads%2Fgit-blob-e31727ce3cf6def295cf9d806d31afba0e9c090d%2FUntitled%204.png?alt=media) ![Linux file structure part 4](https://473782116-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2F-MlTUR0kU-pvc2XyvuDJ%2Fuploads%2Fgit-blob-2cce48493031003c56f7ed0fc7d5435054d00eac%2FUntitled%205.png?alt=media) ![Linux file structure part 5](https://473782116-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2F-MlTUR0kU-pvc2XyvuDJ%2Fuploads%2Fgit-blob-4c307f62ad04e532de7e5b6bcd28647eff645cba%2FUntitled%206.png?alt=media) ## Symbolic Links | Soft Link | Symlink * symbolic links are like aliases or another name for the file ```java lrwxrwxrwx 1 root root 11 2018-08-11 07:34 libc.so.6 ***->*** libc-2.6.so ``` **Why they are useful ?** * Imagine we have a file with name `foo` . Whenever we update it we, change its name to foo-date-time, but the programs/user referencing it wouldst know that the name has change. To tackle this problem, we create a symlink of file foo → foo-date-time and the programs/user user only reference the symlink. * So even if we change the name of file foo, it wont affect the programs as they would be referencing the symlink. ## Manipulating Files and Directories * to create new directories * `mkdir dir_name` * to create multiple directories * `mkdir dir1 dir2 dir3` * to copy file to another directory * `cp item directory` * if `cp item1 item2` then content of item2 is replace with item1 * use `-a` file while copying to copy the attributes as well ![options for cp command](https://473782116-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2F-MlTUR0kU-pvc2XyvuDJ%2Fuploads%2Fgit-blob-bf4a3a5519e44316e5da0d114f71c1e832e2025a%2FUntitled%207.png?alt=media) * The `mv` command performs both file moving and file renaming, depending on how it is used * to move item to another directory `mv item... directory` * to delete item `rm item` ![options for rm command](https://473782116-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2F-MlTUR0kU-pvc2XyvuDJ%2Fuploads%2Fgit-blob-976f68e638f08a6cebd2884c9539e1ffde6d88fb%2FUntitled%208.png?alt=media) ## Hard Links vs Soft Links ### Hard Link * Hard links are the original Unix way of creating links * Every file has a single hard link that gives the file its name * Limitations * A hard link cannot reference a file outside its own file system * A hard link may not reference a directory * A hard link is indistinguishable from the file itself ```bash // for hard link -> ln file.txt link -> ls -rw-r--r--. 1 udayyadav udayyadav 12 Jun 20 23:06 file.txt -rw-r--r--. 2 udayyadav udayyadav 12 Jun 20 23:06 link1 ``` ### Soft Link * They work by creating a special type of file that contains a text pointer to the referenced file or directory * They are like windows shortcuts * If file is deleted, then link points to nothing, it is broken ```bash // for soft link -> ln -s file.txt link -> ls lrwxrwxrwx. 1 udayyadav udayyadav 9 Jun 21 07:59 link2 -> file2.txt ``` ## WildCards ![different wildcards present](https://473782116-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2F-MlTUR0kU-pvc2XyvuDJ%2Fuploads%2Fgit-blob-e4d9a3f20aa6aef72fa86ecf0ccb306d95d8edf4%2FUntitled%209.png?alt=media) ![matching with different characters](https://473782116-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2F-MlTUR0kU-pvc2XyvuDJ%2Fuploads%2Fgit-blob-a46cc42217100c681ab7d2138ab0d45ee3953c09%2FUntitled%2010.png?alt=media) ![wildcard example](https://473782116-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2F-MlTUR0kU-pvc2XyvuDJ%2Fuploads%2Fgit-blob-d869b989c138eb02cb86b5b7836c878f3bd80842%2FUntitled%2011.png?alt=media)