rcanepa

$ jot - 1 5
         ^
    return numbers from 1 to 5
1
2
3
4
5

$ jot -b "#" - 1 5

rcanepa

```
$ (cd src && tar -c .) | (cd dst && tar -xp)
          1^           2^        3^
```

1^ this fork a new process that execute those commands and use the writing end of the pipe as its STDOUT
2^ the pipe has two ends (to write and read), and both of them have a fd
3^ this fork a new process that execute those commands using the reading end of the pipe as its STDIN

Also, using && instead of ; to separate commands means that if the first one fails, the second one won't be executed. 

rcanepa

Bash accomodates piping and redirection by way of special files. Each process gets it's own set of files (one for STDIN, STDOUT and STDERR respectively) and they are linked when piping or redirection is invoked. Each process gets the following files:

STDIN - /proc//fd/0 STDOUT - /proc//fd/1 STDERR - /proc//fd/2

To make life more convenient the system creates some shortcuts for us:

STDIN - /dev/stdin or /proc/self/fd/0 STDOUT - /dev/stdout or /proc/self/fd/1

rcanepa

#awk In awk, a file is treated as a sequence of records, and by default each line is a record and every word is a field.

$ cat text
this is the first line
second one
third one
who cares anymore?
....

rcanepa

$ cd /tmp/
$ echo '10 tiny toes' >> text
$ echo 'this is that' >> text
$ echo '5 funny 0' >> text
$ echo 'one two three' >> text
$ echo 'tree twice' >> text

$ cat text
10 tiny toes
this is that

rcanepa

- Count the number of namespaces
1) find all .clj files under src/scv2backend/ directory, 
2) find all the lines which contains the words 'ns scv2', 
3) split the line by a white space and return the second half, 
4) count the number of lines

find src/scv2backend/ -name '*.clj' | 
  xargs grep -h 'ns scv2' |
  cut -d ' ' -f 2 | 
  wc -l

rcanepa

- diff processes outputs
$ diff -u <(ps aux) <(ps aux)
--- /dev/fd/63	2016-08-06 01:02:53.000000000 -0400
+++ /dev/fd/62	2016-08-06 01:02:53.000000000 -0400
@@ -312,12 +312,12 @@
 root               44   0.0  0.0  2518564   1944   ??  Ss   Wed07PM   0:45.29 /usr/sbin/syslogd
 root               43   0.0  0.1  2551932  10704   ??  Ss   Wed07PM   0:23.84 /usr/libexec/UserEventAgent (System)
 root                1   0.0  0.1  2538696  11456   ??  Ss   Wed07PM   5:36.04 /sbin/launchd
-root            20967   0.0  0.0  2435076   1016 s001  R     1:02AM   0:00.00 ps aux
+root            20967   0.0  0.0  2435232   1032 s001  R     1:02AM   0:00.00 ps aux

rcanepa

Grep searches strings/patterns inside other strings/text.

Basic usage:
grep some-string some-file

-> This will return all lines of the file named 'some-file' which contains the string 'some-string'.

ls | grep some-string

-> This will return all files which contains the string 'some-string' in their names

rcanepa

- fetch a git commit log
git log -1 <hash>

- fetch commit list (reversed: last one is first)
git rev-list HEAD

- execute git log for every commit (on the reversed commit list)
git rev-list --reverse HEAD | while read rev; do git log -1 $rev; done

- print file tree for every commit

rcanepa

grep -rnw . -e ".*\.extend" --include=\*.js

-r or -R is recursive,
-n is line number, and
-w stands match the whole word.
-l (lower-case L) can be added to just give the file name of matching files.

More examples

grep --include=\*.{c,h} -rnw '/path/to/somewhere/' -e "pattern"