GNU/Linux

How to find lines that contain only lowercase characters

 in Bash  tagged grep / lower case / lowercase / regex / regular expression by

To print all lines that contain only lower case characters, we used the following regular expression in grep:


egrep '^[[:lower:]]+$' <file>;
#If you do not have egrep, use
grep -e '^[[:lower:]]+$' <file>;

Breakdown of the above regular expression:

  • ^ instructs the regular expression parser that the pattern should always start with the beginning of the line
  • [[:lower:]] this special instruction informs us that only lower case characters can match it
  • + the plus sign causes the preceding token to be matched one or more times
  • $ signifies the end of the line

How to create a compressed archive for each folder in current directory

 in GNU/Linux  tagged compression / current date / find / lossless / metadata / tar / xz by

The following command will create a compressed tar archive for each folder found in the current directory.
It will use the LZMA/LZMA2 compression algorithms and it supports Unix-like file system metadata as well.
It will reuse the name of the folder for the archive as well and it will append the current date to the name.


find . -maxdepth 1 -mindepth 1 -type d -exec tar cJf "{}.`date +%F`.tar.xz" '{}' \;

The parameters we used for the find command are the following:

  • -maxdepth levels Descend at most levels (a non-negative integer) levels of directories below the command line arguments. -maxdepth 0 means only apply the tests and actions to the command line arguments.
  • -mindepth levelsDo not apply any tests or actions at levels less than levels (a non-negative integer). -mindepth 1 means process all files except the command line arguments.
  • -type d Match directories (folders) only

The parameters we used for the tar command are the following:

CentOS 6: install / start and stop / enable and disable ssh server

 in GNU/Linux  tagged chkconfig / fedora / openssh-server / server / ssh / system by

Install

To install the openssh-server, you need to install the openssh-server package:

sudo yum install -y openssh-server;

Start

To start the sshd daemon (openssh-server) in the current session:

sudo service sshd start;

Stop

To stop the active (if any) sshd daemon in the current session:

sudo service sshd stop;

Enable

To configure the sshd daemon to start automatically at boot time:

sudo chkconfig sshd --add;
sudo chkconfig sshd on --level 2,3,4,5;

Disable

To configure the sshd daemon to stop automatic initialization at boot time:

sudo chkconfig sshd off;
sudo chkconfig sshd --del;

Fedora 26: C++: static linking cannot find -lstdc++ -lm and -lc

 in Bash / GNU/Linux / Programming  tagged C++ / dnf / fedora / g++ / glibc / glibc-static / lc / libstdc / libstdc++-static / lm / lstdc / static by

Recently, we were trying to compile a C++ application with the following compilation command on a Fedora 26 64bit :


g++ -static -O2 -lm -Wall -Wno-unused-result -std=c++14 -DCS_ACADEMY -DONLINE_JUDGE 510152025.cpp -o 510152025;

unfortunately, we got the following errors:

 /usr/bin/ld: cannot find -lstdc++
 /usr/bin/ld: cannot find -lm
 /usr/bin/ld: cannot find -lc
 collect2: error: ld returned 1 exit status

To resolve the issues, we performed the following installations to install the static versions of the glibc and libstdc libraries:


sudo dnf install glibc-static libstdc++-static -y;