diff options
| -rw-r--r-- | A nice way to select IPv4 addresses with JQ.md (renamed from Examples of proper JQ usage.md) | 2 | ||||
| -rw-r--r-- | Bash process substition (tmp file).md | 13 | ||||
| -rw-r--r-- | Bash.md | 6 | ||||
| -rw-r--r-- | Building a command-line using arrays.md | 34 | ||||
| -rw-r--r-- | Globbing patterns.md | 3 | ||||
| -rw-r--r-- | Heredoc.md | 23 | ||||
| -rw-r--r-- | Nova compute evacuation.md | 10 | ||||
| -rw-r--r-- | Null substitution.md | 25 | ||||
| -rw-r--r-- | Parameter subsitution.md | 8 | ||||
| -rw-r--r-- | Process substition (tmp file).md | 15 | ||||
| -rw-r--r-- | Setting traps.md | 10 | ||||
| -rw-r--r-- | Shell.md | 5 | ||||
| -rw-r--r-- | daily/20-May-2025.md | 0 | ||||
| -rw-r--r-- | daily/27-May-2025.md | 4 |
14 files changed, 144 insertions, 14 deletions
diff --git a/Examples of proper JQ usage.md b/A nice way to select IPv4 addresses with JQ.md index 2b68d01..b8f751d 100644 --- a/Examples of proper JQ usage.md +++ b/A nice way to select IPv4 addresses with JQ.md @@ -6,7 +6,7 @@ tags: Double escapes are important! ``` -jq -r '.fixed_ips[] | select(.ip_address | test("\\.")) | .ip_address' +jq -r '.fixed_ips[] | select(.ip_address | test("([0-9]+\\.)+")) | .ip_address' ``` An example of constructing an array from stdin and filtering empty lines is found in [[Using JQ to construct an array and filtering empty strings]].
\ No newline at end of file diff --git a/Bash process substition (tmp file).md b/Bash process substition (tmp file).md deleted file mode 100644 index 3540f70..0000000 --- a/Bash process substition (tmp file).md +++ /dev/null @@ -1,13 +0,0 @@ ---- -tags: - - bash - - howto ---- -Process substitution connects the output of a command to a file. This enables a command to accept the output of multiple commands. -Useful with diff for example: - -```bash -diff <(ls dirA) <(ls dirB) -``` - -> Important! Don't but the <() inside quotes.. it will report: cannot find file
\ No newline at end of file @@ -0,0 +1,6 @@ +--- +tags: + - bash +--- +A scripting language in which a user can string together [[Shell]] commands in a reusable file called a script. The script can be executed (or "called") and it will execute the string of commands. +They are not full general purpose programming languages, even though they often have similar constructs available.
\ No newline at end of file diff --git a/Building a command-line using arrays.md b/Building a command-line using arrays.md new file mode 100644 index 0000000..8e187c7 --- /dev/null +++ b/Building a command-line using arrays.md @@ -0,0 +1,34 @@ +--- +tags: + - bash +--- +[[Bash]] [[Globbing patterns]] + +--- +See https://www.shellcheck.net/wiki/SC2086 + +issue with building a command-line and prevent globbing by quoting parameter expansion, solution: use array. + +``` +#!/usr/bin/env bash +function test() { + echo "${@}" +} +function blaat() { + local flags + test hello "${flags[@]}" +} +function blaat1() { + local flags + flags=(a b c) + test hello "${flags[@]}" +} +blaat +blaat1 +``` + +``` +❯ bash /tmp/tmp.qI8lPlBQUe +hello +hello a b c +```
\ No newline at end of file diff --git a/Globbing patterns.md b/Globbing patterns.md index 12b7582..bc7534c 100644 --- a/Globbing patterns.md +++ b/Globbing patterns.md @@ -2,6 +2,9 @@ tags: - linux --- +[[Bash]] + +--- https://linux.die.net/man/7/glob **Wildcards** diff --git a/Heredoc.md b/Heredoc.md new file mode 100644 index 0000000..84c0fa5 --- /dev/null +++ b/Heredoc.md @@ -0,0 +1,23 @@ +--- +tags: + - bash +--- +[[Bash]] + +--- +``` +read -r -d '' VAR <<EOF +blaat +EOF +``` + +``` +var=$( +cat <<EOF +blaat +EOF +) +``` + +Quote EOF/NAME to prevent expansion +Put - after << to remove indentation from result
\ No newline at end of file diff --git a/Nova compute evacuation.md b/Nova compute evacuation.md new file mode 100644 index 0000000..409ea42 --- /dev/null +++ b/Nova compute evacuation.md @@ -0,0 +1,10 @@ +--- +tags: + - openstack +--- +To evacuate a compute node we can `nova host-evacuate <hostname>`. I did it like this on the access node: +``` +nova --os-token gAAAAABoLXVPU1N-pYc8Xm7ypmWZX_hSuy7psMS_kudoYg6msHZdXYk_dordZB8Imm6-PT8916iPH5n9BvYLmHAQl7UGHuSNsfHZH8k_s1EPbfU8aE15s8Hu0ngNLW2amv_C-peJ8BZLHIl3K7cz2b05D0wRDnzbWl0h0w5NyY6aY_8YcMkVIzc --os-project-name hostnet --os-auth-url https://keystone.os1.openstack.group.one:5000/v3 host-evacuate n28.compute.env.vps1-cph8.one.com +``` + +[This](https://www.danplanet.com/blog/2016/03/03/evacuate-in-nova-one-command-to-confuse-us-all/) webpage has some useful information on evacuation in its different forms.
\ No newline at end of file diff --git a/Null substitution.md b/Null substitution.md new file mode 100644 index 0000000..276a2e6 --- /dev/null +++ b/Null substitution.md @@ -0,0 +1,25 @@ +--- +tags: + - bash +--- +[[Bash]] [[Process substition (tmp file)]] [[Parameter subsitution]] + +--- +[This](https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_06_02) page contains a table with [[Parameter subsitution]] + +When we want to expand a variable into an argument to a command but the variable is empty it will expand to **an empty string**. This is often unwanted, we just want `null` which is removed from the command-line. + +*Example* +``` +openstack server delete server "${waitFlag}" +``` +if `waitFlag` is empty this will become: +``` +openstack server delete server '' +``` +which results in an error. + +This is where we can use `null substitution`: +``` +openstack server delete server "${waitFlag:+$waitFlag}" +```
\ No newline at end of file diff --git a/Parameter subsitution.md b/Parameter subsitution.md new file mode 100644 index 0000000..c50f231 --- /dev/null +++ b/Parameter subsitution.md @@ -0,0 +1,8 @@ +--- +tags: + - bash +--- +[[Bash]] [[Null substitution]] [[Process substition (tmp file)]] + +--- +[This](https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_06_02) page contains a useful table.
\ No newline at end of file diff --git a/Process substition (tmp file).md b/Process substition (tmp file).md new file mode 100644 index 0000000..c9103c2 --- /dev/null +++ b/Process substition (tmp file).md @@ -0,0 +1,15 @@ +--- +tags: + - bash + - howto +--- +[[Bash]] [[Parameter subsitution]] [[Null substitution]] + +Process substitution connects the output of a command to a file. This enables another command to accept the output of multiple commands as files if it expects files. + +An example of this is `diff`, which outputs the difference between two files: +```bash +diff <(ls dirA) <(ls dirB) +``` + +> Important! Don't but the <() inside quotes.. it will report: cannot find file
\ No newline at end of file diff --git a/Setting traps.md b/Setting traps.md new file mode 100644 index 0000000..cd36e80 --- /dev/null +++ b/Setting traps.md @@ -0,0 +1,10 @@ +--- +tags: + - bash +--- +With traps you can configure a function that is run upon a specific signal or when the script fails or exits normally. + +`trap fn ERR` > when an error occurrs +`trap fn EXIT` > any exit, also errors and interrupts +`trap fn SIGINT` > when interrupted +`trap fn ERR SIGINT` > either an interrupt or error occurred
\ No newline at end of file diff --git a/Shell.md b/Shell.md new file mode 100644 index 0000000..ed90df2 --- /dev/null +++ b/Shell.md @@ -0,0 +1,5 @@ +--- +tags: + - linux +--- +A shell is a command-line interface; it interprets textual instructions (commands) to the operating system.
\ No newline at end of file diff --git a/daily/20-May-2025.md b/daily/20-May-2025.md new file mode 100644 index 0000000..e69de29 --- /dev/null +++ b/daily/20-May-2025.md diff --git a/daily/27-May-2025.md b/daily/27-May-2025.md new file mode 100644 index 0000000..908736b --- /dev/null +++ b/daily/27-May-2025.md @@ -0,0 +1,4 @@ +Decided that devenv is too invasive for use at work; I can't commit its .envrc nor .pre-commit-config.yaml. Therefore I'm setting up just regular shell.nix usage. I quickly ran into an issue where the nix shell is using bash and found a tool called Lorri which promises to be useful for developer environments with shell.nix. Let's hope that is less invasive than devenv. +Thus far it's not very nice, it install stuff on the background ( a systemd daemon that listens for change ) of which you have no idea when its done. + +TIL: gitlab ci job can specify `resource_group` to make it mutually exclusive with other jobs that have this resource group.
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