Differences

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--- bash:files:read_a_file:read_fields_from_a_file [2021/01/26 13:25] – peter
+++ bash:files:read_a_file:read_fields_from_a_file [2021/01/26 13:44] (current) – [Field splitting, white-space trimming, and other input processing] peter
@@ Line 30: / Line 30: @@
 <WRAP info>
-**NOTE:**  IFS is set to **:**.
+**NOTE:**  IFS is set to a colon, **:**, as every field in the passwd file is separated by a colon.
+</WRAP>
+----
+===== Tab-delimited files =====
+<WRAP info>
+**NOTE:**  For tab-delimited files, use **IFS=$'\t'**.
+<WRAP important>
+**WARNING:**  Multiple tab characters in the input will be considered as one delimiter (and the **IFS=$'\t\t'** workaround does not work in Bash).
+</WRAP>
+</WRAP>
+----
-For tab-delimited files, use **IFS=$'\t'** though beware that multiple tab characters in the input will be considered as one delimiter (and the **IFS=$'\t\t'** workaround will not work in Bash).
+===== Not knowing how many fields a line contains =====
 You do not necessarily need to know how many fields each line of input contains.
@@ Line 42: / Line 59: @@
 <code bash>
-read -r first last junk <<< 'Bob Smith 123 Main Street Elk Grove Iowa 123-555-6789'
+read -r first last junk <<< 'Bob Smith 123 Main Street Saint Helier Jersey'
 </code>
+<WRAP info>
+**NOTE:**
   * **first**:   will contain "Bob"
@@ Line 49: / Line 69: @@
   * **junk**:  holds everything else.
-The throwaway variable **_** can be used as a "junk variable" to ignore fields.
+</WRAP>
+----
-  * It (or indeed any variable) can also be used more than once in a single read command, if we don't care what goes into it:
+===== Throwaway variable =====
 <code bash>
@@ Line 57: / Line 79: @@
 </code>
-  * We skip the first two fields, then read the next three.
-  * The final **_** can absorb any number of fields.
+<WRAP info>
+**NOTE:**  The throwaway variable **_** can be used as a "junk variable" to ignore fields.
+  * It, and any other variable, can be used more than once in a single read command, if we don't care what goes into it.
+  * The first two fields are skipped.
+  * The next three fields are reading into variables.
+  * The final **_** will absorb any remaining fields on the line.
     * It does not need to be repeated there.
-This usage of **_** is only guaranteed to work in Bash.
+<WRAP important>
+**WARNING:**  This usage of **_** is only guaranteed to work in Bash.
-  * Many other shells use _ for other purposes that will at best cause this to not have the desired effect, and can break the script entirely.
+  * Many other shells use **_** for other purposes that will at best cause this to not have the desired effect, and can break the script entirely.
-  * It is better to choose a unique variable that isn't used elsewhere in the script, even though _ is a common Bash convention.
+  * It is better to choose a unique variable that isn't used elsewhere in the script, even though **_** is a common Bash convention.
+</WRAP>
 </WRAP>
+----