Shell/bash course
https://urfist.unistra.fr/uploads/media/command_memento_fr.pdf
- BSD: berkely univsersity. public/research
- system V: private, constructors: DEC, SUN
- POSIX: standard on all system
Change shell
usermod -s /bin/bash formation
chsh
[root@localhost ~]# useradd ben
[root@localhost ~]# passwd ben
Changement de mot de passe pour l'utilisateur ben.
Nouveau mot de passe :
MOT DE PASSE INCORRECT : Le mot de passe comporte moins de 8 caractères
Retapez le nouveau mot de passe :
passwd : mise à jour réussie de tous les jetons d'authentification.
[root@localhost ~]# usermod -s /bin/ksh ben
[root@localhost ~]# tail -4 /etc/passwd
tcpdump:x:72:72::/:/sbin/nologin
formation:x:1000:1000:Formation:/home/formation:/bin/bash
vboxadd:x:988:1::/var/run/vboxadd:/bin/false
ben:x:1001:1001::/home/ben:/bin/ksh
Switch user: su
Make use of the - to get user env
[root@localhost ~]# su - ben
Dernière connexion : lundi 7 octobre 2019 à 09:46:27 CEST sur pts/0
Text shell
ctrl + alt + F1 => graphical shell mode
ctrl + alt + F[2-6] => text shell mode
File type
- file
d directory
l link
c char I/O hardware
b block I/O hardware
p pipe : inter process (local)
s socket : inter process (network)
tty
terminal teletype
[formation@localhost ~]$ tty
/dev/pts/0
[formation@localhost ~]$ echo "hello"
hello
[formation@localhost ~]$ echo "hello" > /dev/pts/1
Env var
available in:
- new window
- new shell
- new script
env: list env var
set: env + pre param shell
File command
[formation@localhost ~]$ file /bin/ls
/bin/ls: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 2.6.32, BuildID[sha1]=c5ad78cfc1de12b9bb6829207cececb990b3e987, stripped
[formation@localhost ~]$ file foo.pdf
foo.pdf: ASCII text
[formation@localhost ~]$ mv foo.pdf foo.md
[formation@localhost ~]$ file foo.md
foo.md: ASCII text
special bits
setuid
when present on an executable file, the programm is executed with the identity of the file owner
[formation@localhost ~]$ which passwd
/usr/bin/passwd
[formation@localhost ~]$ ls -l /usr/bin/passwd
-rwsr-xr-x. 1 root root 27832 10 juin 2014 /usr/bin/passwd
chmod 4555 prog.sh
[formation@localhost ~]$ ls -l prog.sh
-r-sr-xr-x. 1 formation formation 0 7 oct. 10:56 prog.sh
setgid
idem for group
sticky bit: t
only owner can destroy folder (add resistance to destruction).
ls -ld /tmp/
drwxrwxrwt. 15 root root 4096 7 oct. 10:59 /tmp/
Groups
create first group
then create user, and assign group
groupadd friends
groupadd painters
useradd foo -g firends -G painters
$PATH
contains paths of executables path
PATH=$PATH:/new/location/exec
find command
find /dev - type l -name "*or*" -exec file {} \;
locate command
locate file2Search
updatedb
Command IO
- stdin: <1
- stdout: >1
- stderr: >2
2>&1: recirect stderr to stdout
1>&2: redirect stdout to stderr
ls -l file 1> out
ls -l file doesNotExist 2> error 1>out
ls -l file &> out
tree
tree of files
pstree
tree of ps
ps clax
ps -ef
bash debug mode
bash -vx script.sh
command return code
$? == 0 ok
$? != 0 ko
logical operators
AND &&
if left part is OK
ls && echo "ls done"
OR ||
if left part fails
ls -l inexistant || echo "inexistant file does not exist"
Together
concatenate if exists,else copy
ls -l mypasswd && cat /etc/passwd >> mypasswd || cp /etc/passwd mypasswd
cut -d":" -f1,3 /etc/passwd | tr ':' ' ' > users-id
cat /etc/group | cut -d":" -f1,3 | sort | nl
cut -d: -f1,3 /etc/group|sort -t: -n -k2 | nl
Terminal movement utilities
ctrl+a
ctrl+e
alt+d
Vim
filetype indent plugin on
gg=G => indent all file
source VS ./
source script: execute in current shell
./script: execute in a child shell
nohut
run a script whithout deconnexion
nohup ./script.sh &
exec command
exec date
print date and kill exit current process
signals
- ctrl + c:
- ctrl + z:
- ctrl + d:
When killing a parent process with child process, children are adopted by systemd PID #1.
example
eyes &
ctrl+d
ps aux
eyes has PPID=1
jobs command
foreground + ctrl-c
[formation@localhost ~]$ xeyes &
[1] 19078
[formation@localhost ~]$ jobs
[1]+ En cours d'exécution xeyes &
[formation@localhost ~]$ fg %1
xeyes
^C
[formation@localhost ~]$
kill it
[formation@localhost ~]$ xeyes &
[1] 19207
[formation@localhost ~]$ kill %1
[1]+ Complété xeyes
trap
[root@localhost ~]# trap -l
1) SIGHUP 2) SIGINT 3) SIGQUIT 4) SIGILL 5) SIGTRAP
6) SIGABRT 7) SIGBUS 8) SIGFPE 9) SIGKILL 10) SIGUSR1
11) SIGSEGV 12) SIGUSR2 13) SIGPIPE 14) SIGALRM 15) SIGTERM
16) SIGSTKFLT 17) SIGCHLD 18) SIGCONT 19) SIGSTOP 20) SIGTSTP
21) SIGTTIN 22) SIGTTOU 23) SIGURG 24) SIGXCPU 25) SIGXFSZ
26) SIGVTALRM 27) SIGPROF 28) SIGWINCH 29) SIGIO 30) SIGPWR
31) SIGSYS 34) SIGRTMIN 35) SIGRTMIN+1 36) SIGRTMIN+2 37) SIGRTMIN+3
38) SIGRTMIN+4 39) SIGRTMIN+5 40) SIGRTMIN+6 41) SIGRTMIN+7 42) SIGRTMIN+8
43) SIGRTMIN+9 44) SIGRTMIN+10 45) SIGRTMIN+11 46) SIGRTMIN+12 47) SIGRTMIN+13
48) SIGRTMIN+14 49) SIGRTMIN+15 50) SIGRTMAX-14 51) SIGRTMAX-13 52) SIGRTMAX-12
53) SIGRTMAX-11 54) SIGRTMAX-10 55) SIGRTMAX-9 56) SIGRTMAX-8 57) SIGRTMAX-7
58) SIGRTMAX-6 59) SIGRTMAX-5 60) SIGRTMAX-4 61) SIGRTMAX-3 62) SIGRTMAX-2
63) SIGRTMAX-1 64) SIGRTMAX
Loop
sequence command
seq 5
1
2
3
4
5
for i in $(seq 5); do echo $i; done
Return code
$?
value ok: 0
shift: process & remove first value of array parameter
shift.sh
#!/bin/bash
while test $# -ne 0
do
echo "current paramater: $1 - nb remaning paramter "$#
shift 1
done
bash shift.sh aa bb cc
current paramater: aa - nb remaning paramter 3
current paramater: bb - nb remaning paramter 2
current paramater: cc - nb remaning paramter 1
arithmetic expression : (( expr ))
echo $(( 2+2+6+6 ))
16
((i=i+1))
