BASH

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BASH – Leaving a line after Cat

If you are writing a script that involve cat and if you wish to leave a line after “cat”, do the following

cat /usr/local/lic_lmstat_log/abaqus_lmstat.log ; echo
.....
.....
Users of tfluid_int_ccmp:  (Total of 128 licenses issued;  Total of 0 licenses in use)

Users of tfluid_int_fluent:  (Total of 128 licenses issued;  Total of 0 licenses in use)
[user1@node1 ~]$
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Shortening BASH Commands (Part 1)

I had a casual read on the book “Bash Idioms” by Carl Albing. I scribbled what I learned from what stuck me the most. There are so much more. Please read the book instead.

Lesson 1: “A And B” are true only if both A and B are true…..

Example 1: If the cd command succeeds, then execute the “rm -Rv *.tmp” command

cd tmp && rm -Rv *.tmp

Lesson 2: If “A is true”, “B is not executed” and vice versa.

Example 2: Change Directory, if fail, put out the message that the change directory failed and exit

cd /tmp || { echo "cd to /tmp failed" ; exit ; }

Lesson 3: When do we use the [ ] versus [[ ]]?

I learned that the author advises BASH users to use the [[ ]] unless when avoidable. The Double Bracket helps to avoid confusing edge case behaviours that a single bracket may exhibit. If however, the main goal is portability across various platform to non-bash platforms, single quota may be advisable.

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Change Runlevel of Rocky Linux 8 without rebooting

You may use the command “telinit” to change the SysV system runlevel without the need to reboot. You will need root access to run the command

Use 1: Single User Mode

# telinit S

Use 2: To go to Graphical.Target

# telinit 5

Use 3: To go to Multi-User.Target

# telinit 3

Use 4: To Reload daemon configuration. This is equivalent to systemctl daemon-reload.

# telinit q

To verify, you can use the command systemctl get-default

# systemctl get-default
graphical.target
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Using Bash alias to keep things simple

Alias are very useful tools to create shorthand pseudonyms to run the command you want without typing the whole thing.

Display all alias names

Typing alias the whole command will 

$ alias
alias cp='cp -i'
alias egrep='egrep --color=auto'
alias fgrep='fgrep --color=auto'
alias grep='grep --color=auto'
alias l.='ls -d .* --color=auto'
alias ll='ls -l --color=auto'
alias ls='ls --color=auto'
alias mv='mv -i'
alias rm='rm -i'
alias xzegrep='xzegrep --color=auto'
alias xzfgrep='xzfgrep --color=auto'
alias xzgrep='xzgrep --color=auto'
alias zegrep='zegrep --color=auto'
alias zfgrep='zfgrep --color=auto'
alias zgrep='zgrep --color=auto'

Useful Alias to consider

alias ls='ls --color=auto'
alias egrep='egrep --color=auto'
alias fgrep='fgrep --color=auto'
alias grep='grep --color=auto'
alias mv='mv -i'
alias rm='rm -i'
alias cp='cp -i'

Remove alias

Just use the command unalias 

unalias ll
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Linux expect and spawn id exp6 not open issue

I was having an issue with my expect script

spawn ssh licensecheck@192.168.1.0
Password:
Authentication failed.
send: spawn id exp6 not open
    while executing
.....
.....

This my code…..

#!/usr/bin/expect
set timeout 20
spawn ssh -o PubkeyAuthentication=no licensecheck@192.168.1.0

expect "Password: " {send "mypassword\r"}
expect "$ " {send "/usr/xxx/xxx/xxx/lmstat -a\r"}
expect "$ " {send "exit\r"}

Do check out whether the expression is correct. In case, I leave a space after “Password: ” After I remove, the space, the error is gone. There is also a write-up in a form. Do take a look at Linux – spawn_id: spawn id exp6 not open

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Using NMCLI to manage Network on Rocky Linux 8

Point 1: View all the saved connections

# nmcli connection show
ens1f0     XXXX-XXXX-XXXX-XXXX-XXXX  ethernet  ens1f0
ens1f1     YYYY-YYYY-YYYY-YYYY-YYYY  ethernet  ens1f1
ens10f0    ZZZZ-ZZZZ-ZZZZ-ZZZZ-ZZZZ  ethernet  --
ens10f1    AAAA-AAAA-AAAA-AAAA-AAAA  ethernet  --

Point 2a: Stop Network

You can use the command “nmcli connection down ssid/uuid". For example 

# nmcli connection down XXXX-XXXX-XXXX-XXXX-XXXX
Connection 'eno0' successfully deactivated (D-Bus active path: /org/freedesktop/NetworkManager/ActiveConnection/3)

Point 2b: Start Network

You can use the command “nmcli connection up ssid/uuid". For example 

# nmcli connection up XXXX-XXXX-XXXX-XXXX-XXXX
Connection 'eno0' successfully activated (D-Bus active path: /org/freedesktop/NetworkManager/ActiveConnection/3)

Point 3: Device Connection

To check the Device status

# nmcli dev status
ens1f0  ethernet  connected     ens1f0
eno1f1  ethernet  connected     ens1f1
eno10f0  ethernet  disconnected  --
eno10f1  ethernet  disconnected  --

Point 4: List all Device 

# nmcli device show
GENERAL.DEVICE:                         ens1f0
GENERAL.TYPE:                           ethernet
GENERAL.HWADDR:                         XX:XX:XX:XX:XX:XX
GENERAL.MTU:                            1500
GENERAL.STATE:                          100 (connected)
GENERAL.CONNECTION:                     ens1f0
GENERAL.CON-PATH:                       /org/freedesktop/NetworkManager/ActiveConnection/2
WIRED-PROPERTIES.CARRIER:               on
IP4.ADDRESS[1]:                         192.168.0.1
IP4.GATEWAY:                            192.168.0.254
IP4.ROUTE[1]:                           dst = 0.0.0.0/0, nh = 192.168.0.254, mt = 101
IP4.ROUTE[2]:                           dst = 198.168.0.0/19, nh = 0.0.0.0, mt = 101
IP6.ADDRESS[1]:                         xxxx::xxxx:xxxx:xxxx:xxxx/64
IP6.GATEWAY:                            --
IP6.ROUTE[1]:                           dst = fe80::/64, nh = ::, mt = 1024

GENERAL.DEVICE:                         eno1f1
GENERAL.TYPE:                           ethernet
GENERAL.HWADDR:                         94:6D:AE:9B:76:1C
GENERAL.MTU:                            1500
GENERAL.STATE:                          100 (connected)
GENERAL.CONNECTION:                     eno1f1
GENERAL.CON-PATH:                       /org/freedesktop/NetworkManager/ActiveConnection/4
WIRED-PROPERTIES.CARRIER:               on
IP4.ADDRESS[1]:                         192.168.200.201/19
IP4.GATEWAY:                            --
IP4.ROUTE[1]:                           dst = 192.168.192.0/19, nh = 0.0.0.0, mt = 102
IP6.ADDRESS[1]:                         fe80::966d:aeff:fe9b:761c/64
IP6.GATEWAY:                            --
IP6.ROUTE[1]:                           dst = fe80::/64, nh = ::, mt = 1024

Point 5: Start and Stop Device 

# nmcli con down ens1d1
# nmcli con up ens1d1

References:

  1. nmcli command in Linux with Examples
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Listing and Sorting Files

Listing files by access date.

You can use the “-ltur” option. The “u” enforces the “by access date” listing order.  The “t” option to list files in order of age. The “r” option is to reverse the option

$ ls -ltur
-rwxr-xr-x  1 user1 users 1622374400 Mar 10 00:08 yyyy.iso
-rw-rw-r--  1 user1 users   18387452 Mar 13 14:06 xxxx.rpm
-rwxr-xr-x  1 user1 users        303 Mar 30 16:32 visJob.pbs
-rw-------  1 user1 users        762 Mar 30 16:35 visJob.o1475403
-rw-------  1 user1 users         59 Mar 30 16:35 visJob.e1475403

Listing Files by Modified Date and Time

You can use the “-ltr” option. The “r” is the reverse order. 

$ ls -ltr
-rw-rw-r--  1 melvin melvin   18387452 Mar 13 14:03 xxxx.rpm
-rwxr-xr-x  1 melvin melvin        303 Mar 13 17:00 vis.pbs
-rw-rw-r--  1 melvin melvin       1084 Mar 23 16:52 yyy.pem

Listing files by owner

Use the output of the ls command to sort and pick out the owner column by adding “-k3” to sort on the third field.

$ ls -l | sort -k3 | more
drwx------  29 www           users                 1005 Sep 20  2022 www-home
drwx------  16 yyy           users                  684 Apr  3 14:07 yyy-home
drwx------  16 zzz           users                  746 Mar 21 11:31 zzz-home

Listing files by group

Sort files by the associated groups, you can pass the output from a long listing to the sort command and tell it to sort on column 4.

$ ls -l | sort -k4 | more
drwx------  29 www           users1                 1005 Sep 20  2022 www-home
drwx------  16 yyy           users2                  684 Apr  3 14:07 yyy-home
drwx------  16 zzz           users3                  746 Mar 21 11:31 zzz-home

Listing files by size

To sort files by Size, use the “-S” Option. If you wish to put the largest files at the end, use the “-r”. Use the “-h” to be human readable. 

ls -lSrh
-rw-rw-r--  1 www users 1.9G Nov 15 11:04 integr8_120.xml.gz
-rw-rw-r--  1 www users 6.0G Jul 26  2022 20220712_msconvert.zip
-rw-rw-r--  1 www users 6.9G May 31  2022 ELECTRONICS.tgz
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Using Find to Search Better

Basic Use of FIND

If you are looking to find a file, one of the most common tools is Find. Here is a recap.

OFILE TYPEDESCRIPTION
1type -fLimits search results to files only
2type -dLimits search results to directories only
3type -lLimits search results to symbolic links only

For example, search for a case-insensitive file named “hello.mov”

$ find $HOME -type -iname "Hello.mov"

Parameters

NOPARAMETERSDESCRIPTION
1-namePerform a case-sensitive search for “files”
2-inamePerform a case-insensitive search for “files”
3size +nMatches files of size larger than size n
4size -nMatches files of size smaller than size n
5-mtime nMatches files or directories whose contents were last modified n*24 hours ago
6-atime nMatches files last access n*24 hours ago

For example, search for all case-insensitive files with the extension *mov 2 days ago

$ find $HOME -type -iname "*.mov" -mtime 2

Operators

S/NOOPERATOREXPLANATION
1-andMatch for both sides of the operators
2-orMatch for either test of the operators
3-noteDon’t match the test of the operators

For example, search for all files with Hello*, but excl ude pdf and jpg

$ find \( -name "Hello*" -mtime 2 \) -and -not \( -iname "*.jpg" -or -iname "*.pdf" \)

When using the () to combine tests, remember to escape the (\) brackets. You will need to leave a space after you open and close the brackets

find -type f -iname "*.mov" -exec chmod +x {} \;

The first part find -type f -iname”*.mov” will not be explained….. Executed commands must end with \; (a backslash and semi-colon) and may use {} (curly braces) as a placeholder for each file that the find command locates.

References:

  1. Linux Format – March Edition
  2. Use the Unix find command to search for files