Chapter1 Beginning Bash

1.1 Decoding the Prompt

root  is all-powerful and can do anything on a typical Unix or Linux system.

~ mean you are in your home directory.

$ indicates this is a regular user, not root.

1.2 Showing Where You Are

pwd stands for print working directory and takes two options.

-L displays your logical path

-P is the default.P displays your physical location.

1.3 Finding and Running Commands

type,which,apropos,locate,slocate,find and ls commands.

[root@MaxwellDBA tmp]# type which
which is a function
which () 
{ 
    ( alias;
    eval ${which_declare} ) | /usr/bin/which --tty-only --read-alias --read-functions --show-tilde --show-dot "$@"
}
[root@MaxwellDBA tmp]# type ls
ls is aliased to `ls --color=auto'
[root@MaxwellDBA tmp]# type -a ls
ls is aliased to `ls --color=auto'
ls is /usr/bin/ls
[root@MaxwellDBA tmp]# which which
which ()
{ 
    ( alias;
    eval ${which_declare} ) | /usr/bin/which --tty-only --read-alias --read-functions --show-tilde --show-dot "$@"
}
[root@MaxwellDBA tmp]# 

1.4 Getting Information About Files

Use the ls,stat,file,or find commands.

[root@MaxwellDBA tmp]# touch /tmp/sample_file
[root@MaxwellDBA tmp]# ls /tmp/sample_file
/tmp/sample_file
[root@MaxwellDBA tmp]# ls -l /tmp/sample_file
-rw-r--r-- 1 root root 0 Jul 21 13:30 /tmp/sample_file
[root@MaxwellDBA tmp]# stat /tmp/sample_file
  File: /tmp/sample_file
  Size: 0               Blocks: 0          IO Block: 4096   regular empty file
Device: fd01h/64769d    Inode: 8579        Links: 1
Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2022-07-21 13:30:59.014117361 +0800
Modify: 2022-07-21 13:30:59.014117361 +0800
Change: 2022-07-21 13:30:59.014117361 +0800
 Birth: 2022-07-21 13:30:59.014117361 +0800
[root@MaxwellDBA tmp]# file /tmp/sample_file
/tmp/sample_file: empty
[root@MaxwellDBA tmp]# file -b /tmp/sample_file
empty
[root@MaxwellDBA tmp]# echo '#!/bin/bash -' > /tmp/sample_file
[root@MaxwellDBA tmp]# 
[root@MaxwellDBA tmp]# file /tmp/sample_file
/tmp/sample_file: Bourne-Again shell script, ASCII text executable
[root@MaxwellDBA tmp]# file -b /tmp/sample_file
Bourne-Again shell script, ASCII text executable
[root@MaxwellDBA tmp]# 

1.5 Showing All Hidden(dot) Files in the Current Directory

[root@MaxwellDBA /]# ls -a
.  ..  .autorelabel  bin  boot  dev  etc  home  lib  lib64  media  mnt  opt  proc  root  run  sbin  srv  sys  tmp  usr  var
[root@MaxwellDBA /]# ls -d .[!.]*
.autorelabel
[root@MaxwellDBA /]# ls -d .??*
.autorelabel
[root@MaxwellDBA /]# ls -d .[!.]* .??* | sort -u
.autorelabel
[root@MaxwellDBA /]# 

1.6 Using Shell Quoting

[maxwell@MaxwellDBA ~]$ echo 'A coffee is $5 for' "$USER" '?!'
A coffee is $5 for maxwell ?!
[maxwell@MaxwellDBA ~]$ echo "A coffee is \$5 for $USER?\!"
A coffee is $5 for maxwell?\!
[maxwell@MaxwellDBA ~]$ echo "A coffee is \$5 for $USER?! "
A coffee is $5 for maxwell?! 
[maxwell@MaxwellDBA ~]$ WRONG
-bash: WRONG: command not found
[maxwell@MaxwellDBA ~]$ # wRONG
[maxwell@MaxwellDBA ~]$ echo "$USER won't pay $5 for coffee."
maxwell won't pay  for coffee.
[maxwell@MaxwellDBA ~]$ # work
[maxwell@MaxwellDBA ~]$ echo "USER won't pay \$5 for coffee."
USER won't pay $5 for coffee.
[maxwell@MaxwellDBA ~]$ #Also works
[maxwell@MaxwellDBA ~]$ echo 'I won'\''t pay $5 for coffee.'
I won't pay $5 for coffee.
[maxwell@MaxwellDBA ~]$ 

1.7 Using or Replacing Built-ins and External Commands

Use the type and which commands to see if a given command exists and whether it is built-in or external.

[maxwell@MaxwellDBA ~]$ type cd
cd is a shell builtin
[maxwell@MaxwellDBA ~]$ type awk
awk is /usr/bin/awk
[maxwell@MaxwellDBA ~]$ which cd
/usr/bin/cd
[maxwell@MaxwellDBA ~]$ which awk
/usr/bin/awk
[maxwell@MaxwellDBA ~]$ 

1.8 Determining If You Are Running Interactively

Use the following case statement:

$- is a string listing of all the current shell option flags,

#!/usr/bin/env bash
# cookbook filename: interactive
 
case "$-" in
    *i*) # Code for interactive shell here
         ;;
    *)   # Code for non-interactive shell here
         ;;   
esac