Which shell I’m in?
$ ps $$
PID TTY STAT TIME COMMAND
2612401 pts/0 Ss 0:00 -csh
$ printf %s\\n "$SHELL"
/bin/csh
How to Set an Environment Variable for Just One Command In csh/tcsh?
Use a subshell:
# (setenv XCATBYPASS "Y"; tabdump site)
Reference:
How to set an environment variable for just one command in csh/tcsh
(Retrieved on Mar 13, 2022)
How to set an Environment Variable for Just One Command in csh/tcsh and Pass It To sudo
% sudo "XCATBYPASS=Y" csh -c 'printf %s\\n "$XCATBYPASS"'
Y
NOTE: This also works if you replace csh with tcsh, or with sh, or with bash. (Tested on FreeBSD 13.0 and RHEL 8.4.)
Reference:
Pass environment variable to sudo
(Retrieved on Mar 13, 2022)
Set the Window Title in xterm(1)
From the man page for xterm(1) (OS: FreeBSD 13):
[...]
For example, to set the window title to "Hello world!", you could use
one of these commands in a script:
printf '\033]2;Hello world!\033\'
printf '\033]2;Hello world!\007'
printf '\033]2;%s\033\' "Hello world!"
printf '\033]2;%s\007' "Hello world!"
The printf command interprets the octal value "\033" for escape, and
(since it was not given in the format) omits a trailing newline from
the output.
Some programs (such as screen(1)) set both window- and icon-titles at
the same time, using a slightly different control sequence:
printf '\033]0;Hello world!\033\'
printf '\033]0;Hello world!\007'
printf '\033]0;%s\033\' "Hello world!"
printf '\033]0;%s\007' "Hello world!"
The difference is the parameter "0" in each command. Most window
managers will honor either window title or icon title. Some will make
a distinction and allow you to set just the icon title. You can tell
xterm to ask for this with a different parameter in the control
sequence:
printf '\033]1;Hello world!\033\' <- The most portable apporach, with the
printf '\033]1;Hello world!\007' <- parameter "1" - asks if the WM allows
printf '\033]1;%s\033\' "Hello world!" <- WM allows setting only the icon title.
printf '\033]1;%s\007' "Hello world!" <- (Four different ways to do it.)
NOTE:
This can be useful even if you don’t use some window decorations (e.g.: no titlebars) in your window manager. For example, in my current setup with twm(1) where I enabled the NoTitle variable in the ~/.twmrc, I still find it useful to sometimes set the window title for some xterm windows as that makes their title visible in TWM’s Icon Manager and that way helps with identifying which server I’m working on.
xterm(1)
Fonts should be fixed width and, if both normal and bold are specified, should have the same size. If only a normal font is specified, it will be used for both normal and bold text (by doing overstriking).
The -e option, if given, must appear at the end of the command line, otherwise the user’s default shell will be started.
Options that start with a plus sign (+) restore the default.
sed(1)
OS: CentOS Linux 7, Shell: bash
$ grep -n ttyS0 /etc/securetty
24:ttyS0
$ sed -n '/ttyS0/p' /etc/securetty
ttyS0
$ sed -n '/ttyS0/=' /etc/securetty
24
Perl
OS: CentOS Linux 5, Shell: bash
You need to prepend the currency symbol (a.k.a. dollar sign) with a backslash (\) in a heredoc.
$ cat << EOF >> perl1.pl
#!/usr/bin/env perl
use strict;
use Getopt::Long;
use File::Basename;
my \$arguments=join(',',@ARGV);
print "\$arguments\n";
EOF
# chmod 0744 perl1.pl
$ ./perl1.pl testArg1 testArg2
testArg1,testArg2
How to Get Physical Block Size in Linux?
# blockdev --getbsz /dev/sda
4096
If filesystem is XFS (property: bsize):
# df -hT
Filesystem Type Size Used Avail Use% Mounted on
devtmpfs devtmpfs 908M 0 908M 0% /dev
tmpfs tmpfs 919M 0 919M 0% /dev/shm
tmpfs tmpfs 919M 8.5M 911M 1% /run
tmpfs tmpfs 919M 0 919M 0% /sys/fs/cgroup
/dev/mapper/centos-root xfs 3.5G 1.3G 2.3G 36% /
/dev/sda1 xfs 1014M 150M 865M 15% /boot
tmpfs tmpfs 184M 0 184M 0% /run/user/0
# xfs_info /dev/mapper/centos-root
meta-data=/dev/mapper/centos-root isize=512 agcount=4, agsize=229120 blks
= sectsz=4096 attr=2, projid32bit=1
= crc=1 finobt=0 spinodes=0
data = bsize=4096 blocks=916480, imaxpct=25
= sunit=0 swidth=0 blks
naming =version 2 bsize=4096 ascii-ci=0 ftype=1
log =internal bsize=4096 blocks=2560, version=2
= sectsz=4096 sunit=1 blks, lazy-count=1
realtime =none extsz=4096 blocks=0, rtextents=0
# xfs_info /dev/mapper/centos-root | grep bsize
data = bsize=4096 blocks=916480, imaxpct=25
naming =version 2 bsize=4096 ascii-ci=0 ftype=1
log =internal bsize=4096 blocks=2560, version=2
# xfs_info /boot | grep bsize
data = bsize=4096 blocks=262144, imaxpct=25
naming =version 2 bsize=4096 ascii-ci=0 ftype=1
log =internal bsize=4096 blocks=2560, version=2
Running Commands on a Remote Machine with ssh(1)
$ ssh user@example.org "df -hT"
user@example.org's password:
Filesystem Type Size Used Avail Use% Mounted on
/dev/sda1 ext3 263G 26G 224G 11% /
tmpfs tmpfs 7.9G 0 7.9G 0% /dev/shm
mgmt:/home nfs 5.0T 1.7T 3.3T 34% /home
mgmt:/global nfs 3.9T 636G 3.3T 16% /global
Delete All Hidden Files with rm(1)
$ ls -alh /mnt/customdvd/
total 8.0K
drwxr-xr-x 2 root root 40 Apr 23 15:54 .
drwxr-xr-x. 5 root root 50 Apr 22 16:17 ..
-rw-r--r-- 1 root root 29 Oct 26 2020 .discinfo
-rw-r--r-- 1 root root 354 Oct 26 2020 .treeinfo
$ ls -lh /mnt/customdvd/.[a-z0-9]*
-rw-r--r-- 1 root root 29 Oct 26 2020 /mnt/customdvd/.discinfo
-rw-r--r-- 1 root root 354 Oct 26 2020 /mnt/customdvd/.treeinfo
$ sudo rm -i /mnt/customdvd/.[a-z0-9]*
rm: remove regular file '/mnt/customdvd/.discinfo'? y
rm: remove regular file '/mnt/customdvd/.treeinfo'? y
$ ls -alh /mnt/customdvd/
total 0
drwxr-xr-x 2 root root 6 Apr 23 15:58 .
drwxr-xr-x. 5 root root 50 Apr 22 16:17 ..
Jekyll Markdown Internal Links - aka Temporarily Disable Tag Processing
How can you link to internal content in Jekyll?
A: You can post internal links by using the following:
[Some Link]{% post_url 2010-07-21-name-of-post %}
Other options:
[Customize CentOS/RHEL DVD ISO for Installation in Text Mode via Serial Console and Test the Image with QEMU](http://localhost:4000/howto/virtualization/rs232serial/cli/terminal/shell/console/sysadmin/server/hardware/2022/03/12/centos-rhel-dvd-iso-customization-testing-with-qemu.html)
[Customize CentOS/RHEL DVD ISO for Installation in Text Mode via Serial Console and Test the Image with QEMU](/howto/virtualization/rs232serial/cli/terminal/shell/console/sysadmin/server/hardware/2022/03/12/centos-rhel-dvd-iso-customization-testing-with-qemu.html)
NOTE: How to actually display these code examples (with curly braces)?
A: Use raw and endraw tags (see below).
Jekyll Docs - Tags Filters:
(Retrieved on Mar 13, 2022)
Jekyll processes all Liquid filters in code blocks
If you are using a language that contains curly braces, you will likely need to place {% raw %} and {% endraw %} tags around your code.
Since Jekyll 4.0, you can add
render_with_liquid: falsein your front matter to disable Liquid entirely for a particular document.
Liquid Documentation: Tags - Template:
(Retrieved on Mar 13, 2022)
raw
Temporarily disables tag processing. This is useful for generating certain content that uses conflicting syntax, such as Mustache or Handlebars.
– References:
Jekyll Documentation - Linking to posts
(Retrieved on Mar 13, 2022)
Jekyll markdown internal links
(Retrieved on Mar 13, 2022)
How to Join Multiple PDF Pages into One PDF Document with Ghostscript
$ gs -q \
-dNOPAUSE -dBATCH -sDEVICE=pdfwrite -sOutputFile=merged.pdf \
page01.pdf page02.pdf page03.pdf page04.pdf page05.pdf