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--- linux:nice-to-know [2018/01/05 18:08] – michael
+++ linux:nice-to-know [2019/05/06 17:33] (current) – michael
@@ Line 1: / Line 1: @@
 ====== Nice to know Stuff ======
-----
 <WRAP center round box 100%>
@@ Line 69: / Line 68: @@
 ----
+<WRAP center round box 100%>
+''<wrap hi>**"grep" the available space from "df" output:**</wrap>''
+<code># df | grep -oP '/sda1.* \K\d+(?=\s+\d+%)'</code>
+<sxh plain; gutter: false; highlight: [1,4]>
+michael@backup-server:~$ df | grep -oP '/sda1.* \K\d+(?=\s+\d+%)'
+994425716
+michael@backup-server:~$ df
+Filesystem                            1K-blocks        Used   Available Use% Mounted on
+/dev/root                              15039728     1152500    13243704   9% /
+devtmpfs                                 470184           0      470184   0% /dev
+tmpfs                                    474792           0      474792   0% /dev/shm
+tmpfs                                    474792        6308      468484   2% /run
+tmpfs                                      5120           4        5116   1% /run/lock
+tmpfs                                    474792           0      474792   0% /sys/fs/cgroup
+/dev/mmcblk0p1                            41853       21327       20526  51% /boot
+tmpfs                                     94956           0       94956   0% /run/user/1001
+/dev/sda1                            1441091564   373256712   994561592  28% /mnt/backup-disk
+</sxh>
+**Explanation:**
+Here, we match /sda3, then as many characters as possible until we find a stretch of numbers (\d+) which is followed by one or more spaces (\s+), then one or more numbers (\d+) and a %. The foo(?=bar) construct is a positive lookahead, it allows you to search for the string foo only if it is followed by the string bar. The \K is a PCRE trick that means "discard anything matched up to this point". Combined with -o, it lets you use strings that precede your pattern to anchor your match but not print them.
+''<wrap em>Without -P, things are trickier. You would need multiple passes. For example:</wrap>''
+<code>df | grep -o '/sda3.*%' | grep -Eo '[0-9]+ *[0-9]+%' | grep -Eo '^[0-9]+'</code>
+</WRAP>
+----
+<WRAP center round box 100%>
+''<wrap hi>**Split text on whitespace in terminal output**</wrap>''
+To split text on whitespace you can use grep. There’s an infinite amount of ways to do this. This is one of them.
+<code># echo 'string --with ###ALLKINDS### 0f ::outputs' | grep -oP '[^\s]+'</code>
+<sxh plain; gutter: false; highlight: [1]>
+# echo 'string --with ###ALLKINDS### 0f ::outputs' | grep -oP '[^\s]+'
+string
+--with
+###ALLKINDS###
+f
+::outputs
+</sxh>
+</WRAP>
+----
+<WRAP center round box 100%>
+''<wrap hi>**curl only write to file if successful status 200**</wrap>''
+Make curl get the contents of a URL and write to file, but only write to file if the response is successful:
+<code># curl -s -S -f -o blackgate-feed.json "$blackgate_rz"</code>
+  * -s keeps curl quiet by hiding progress meter and error messages
+  * -S shows an error message if it fails (stderr)
+  * -f Fail silently (no output at all) on server errors, keeping stdout clean
+  * -o specifies an output file
+</WRAP>
+----
+<WRAP center round box 100%>
+''<wrap hi>**Pipe video stream from raspberry pi to local computer with ffplay**</wrap>''
+I use this to get a live video stream from my Raspberry Pi with Camera attached
+Execute this on the Pi, where TARGET_IP is my local computer where I will watch the stream, and PORT is an arbitrary port number.
+<code># raspivid -t 999999 -o - | nc -u $TARGET_IP $PORT</code>
+Execute this on the local computer where you will watch the video stream
+<code># nc -ul $PORT | ffplay -</code>
+----
+  * https://www.raspberrypi.org/blog/camera-board-available-for-sale/
+  * https://blog.philippklaus.de/2013/06/using-the-raspberry-pi-camera-board-on-arch-linux-arm/
+</WRAP>
+----
+<WRAP center round box 100%>
+''<wrap hi>**Generating a pseudorandom password or string in Linux bash**</wrap>''
+''Define a function in e.g. **~/.bashrc**''
+<sxh plain; gutter: false;>
+genpasswd() {
+  tr -dc A-Za-z0-9 < /dev/urandom | head -c ${1:-36} | xargs
+}
+</sxh>
+Where 36 is default length if no parameter is given
+----
+**Usage**:
+<code># genpasswd
+GVQ3ZHqrBRDzB1QwASA9uk6YsZPto2GWeRWR
+# genpasswd 7
+qvPWx7N</code>
+</WRAP>