Autosave: 2025-02-22 10:17:45

neuron/d01ec7d6-3cb6-49cf-8ad7-eac41eb5b055/Associative_arrays_maps_in_Bash.md

@@ -0,0 +1,23 @@
+---
+tags: [shell]
+created: Wednesday, February 19, 2025
+---
+
+# Associative arrays (lookup maps) in Bash
+
+```sh
+
+declare -A CHANNEL_TO_WEBHOOK # Declare the map type
+
+# Specify key values
+CHANNEL_TO_WEBHOOK["test"]=$SLACK_WEBHOOK_TEST
+CHANNEL_TO_WEBHOOK["backups"]=$SLACK_WEBHOOK_BACKUPS
+CHANNEL_TO_WEBHOOK["eolas"]=$SLACK_WEBHOOK_EOLAS
+CHANNEL_TO_WEBHOOK["website"]=$SLACK_WEBHOOK_SYSTEMS_OBSCURE
+CHANNEL_TO_WEBHOOK["time-tracking"]=$SLACK_WEBHOOK_TIME_TRACKING
+
+# Invoke
+
+WEBHOOK=${CHANNEL_TO_WEBHOOK[$CHANNEL]}
+
+```

neuron/d01ec7d6-3cb6-49cf-8ad7-eac41eb5b055/Capturing_program_error_in_Bash.md

@@ -0,0 +1,44 @@
+---
+tags: [shell]
+created: Saturday, February 22, 2025
+---
+
+# Capturing program error in Bash
+
+If you want to capture possible error immediately after running the command, use
+`!`:
+
+```sh
+if ! grep "pattern" file.txt; then
+    echo "Pattern not found"
+fi
+```
+
+If you want to store the outcome of a command and refer to it later, use `$?`.
+This built-in variable captures the exit status of the last executed command (0
+for success, non-zero for failure):
+
+```sh
+ls -a
+status=$?  # Store immediately if needed later
+if [ $status -ne 0 ]; then
+    # handle the error case
+else
+    # command was successful (exit code = 0)
+fi
+```
+
+Note: `$?` will be overwritten by any command that runs after the one you're
+interested in. If you need to check multiple commands' statuses, store $?
+immediately after each command:
+
+```sh
+command1
+status1=$?
+command2
+status2=$?
+
+if [ $status1 -ne 0 ] || [ $status2 -ne 0 ]; then
+    echo "One of the commands failed"
+fi
+```

neuron/d01ec7d6-3cb6-49cf-8ad7-eac41eb5b055/Check_if_value_null_in_Bash.md

@@ -0,0 +1,14 @@
+---
+tags: [shell]
+created: Wednesday, February 19, 2025
+---
+
+# Check if value is null in Bash
+
+```sh
+if [ -z $var ]; then
+  # Value is null
+else
+  # Value is not null
+fi
+```

neuron/d01ec7d6-3cb6-49cf-8ad7-eac41eb5b055/index.md

@@ -13,12 +13,16 @@ computer science.
 
 <a href="https://thomasabishop.github.io/eolas/tags">View tags</a>
  
-**Build ID:** 5ce25cd2-1b2b-459a-bb58-283daadf8753
+**Build ID:** d01ec7d6-3cb6-49cf-8ad7-eac41eb5b055
 
-**Published:** Sun 16 Feb 2025 15:17:20
+**Published:** Sat 22 Feb 2025 10:17:40
 
 ### Recent edits 
 
+- [[Capturing_program_error_in_Bash]] 
+- [[Check_if_value_null_in_Bash]] 
+- [[Associative_arrays_maps_in_Bash]] 
+- [[Case_statements_in_Bash]] 
 - [[UFW_firewall_management]] 
 - [[Firewalls]] 
 - [[Disable_non-root_ssh_access]] 
@@ -27,13 +31,9 @@ computer science.
 - [[Let's_Encrypt]] 
 - [[Certificate_authorities]] 
 - [[HTTPS]] 
-- [[Bash_colour_output]] 
-- [[e383b8b3_nginx_vs_traefik]] 
-- [[Proxies]] 
-- [[LineageOS_backup]] 
 
 
-### All notes (530) 
+### All notes (533) 
 
 - [[0716531c_rewilding_the_internet]] 
 - [[241fe1a3_the_Web_versus_modem_BBSs]] 
@@ -76,6 +76,7 @@ computer science.
 - [[Arrays]] 
 - [[Assembly]] 
 - [[Associative_Property_of_Addition_and_Multiplication]] 
+- [[Associative_arrays_maps_in_Bash]] 
 - [[Atomic_and_molecular_propositions]] 
 - [[Audio_file_formats]] 
 - [[Awk]] 
@@ -110,10 +111,12 @@ computer science.
 - [[Bus]] 
 - [[CPU_architecture]] 
 - [[Call_stack]] 
+- [[Capturing_program_error_in_Bash]] 
 - [[Capturing_user_input_in_Bash]] 
 - [[Case_statements_in_Bash]] 
 - [[Cells_and_batteries]] 
 - [[Certificate_authorities]] 
+- [[Check_if_value_null_in_Bash]] 
 - [[Cherry_picking]] 
 - [[Child_to_parent_data_flow_in_React]] 
 - [[Chipset_and_controllers]] 

neuron/d01ec7d6-3cb6-49cf-8ad7-eac41eb5b055/tags.md

@@ -1034,12 +1034,15 @@ unlisted: true
 - [[Basic_properties_of_sets]] 
 ### shell 
 
+- [[Associative_arrays_maps_in_Bash]] 
 - [[Awk]] 
 - [[Bash_colour_output]] 
 - [[Bash_file_exists]] 
 - [[Bash_store_status_of_command_execution]] 
+- [[Capturing_program_error_in_Bash]] 
 - [[Capturing_user_input_in_Bash]] 
 - [[Case_statements_in_Bash]] 
+- [[Check_if_value_null_in_Bash]] 
 - [[Conditionals_in_Bash]] 
 - [[Cron]] 
 - [[Data_types_in_Bash]] 

zk/Associative_arrays_maps_in_Bash.md

@@ -0,0 +1,23 @@
+---
+tags: [shell]
+created: Wednesday, February 19, 2025
+---
+
+# Associative arrays (lookup maps) in Bash
+
+```sh
+
+declare -A CHANNEL_TO_WEBHOOK # Declare the map type
+
+# Specify key values
+CHANNEL_TO_WEBHOOK["test"]=$SLACK_WEBHOOK_TEST
+CHANNEL_TO_WEBHOOK["backups"]=$SLACK_WEBHOOK_BACKUPS
+CHANNEL_TO_WEBHOOK["eolas"]=$SLACK_WEBHOOK_EOLAS
+CHANNEL_TO_WEBHOOK["website"]=$SLACK_WEBHOOK_SYSTEMS_OBSCURE
+CHANNEL_TO_WEBHOOK["time-tracking"]=$SLACK_WEBHOOK_TIME_TRACKING
+
+# Invoke
+
+WEBHOOK=${CHANNEL_TO_WEBHOOK[$CHANNEL]}
+
+```

zk/Capturing_program_error_in_Bash.md

@@ -0,0 +1,44 @@
+---
+tags: [shell]
+created: Saturday, February 22, 2025
+---
+
+# Capturing program error in Bash
+
+If you want to capture possible error immediately after running the command, use
+`!`:
+
+```sh
+if ! grep "pattern" file.txt; then
+    echo "Pattern not found"
+fi
+```
+
+If you want to store the outcome of a command and refer to it later, use `$?`.
+This built-in variable captures the exit status of the last executed command (0
+for success, non-zero for failure):
+
+```sh
+ls -a
+status=$?  # Store immediately if needed later
+if [ $status -ne 0 ]; then
+    # handle the error case
+else
+    # command was successful (exit code = 0)
+fi
+```
+
+Note: `$?` will be overwritten by any command that runs after the one you're
+interested in. If you need to check multiple commands' statuses, store $?
+immediately after each command:
+
+```sh
+command1
+status1=$?
+command2
+status2=$?
+
+if [ $status1 -ne 0 ] || [ $status2 -ne 0 ]; then
+    echo "One of the commands failed"
+fi
+```

zk/Check_if_value_null_in_Bash.md

@@ -0,0 +1,14 @@
+---
+tags: [shell]
+created: Wednesday, February 19, 2025
+---
+
+# Check if value is null in Bash
+
+```sh
+if [ -z $var ]; then
+  # Value is null
+else
+  # Value is not null
+fi
+```