tr: add notes

2 files changed, 40 insertions, 0 deletions

diff --git a/src/cli/README.md b/src/cli/README.md
index 53c64b7..2625899 100644
--- a/src/cli/README.md
+++ b/src/cli/README.md
@@ -4,3 +4,4 @@
 - [sed](./sed.md)
 - [column](./column.md)
 - [sort](./sort.md)
+- [tr](./tr.md)
diff --git a/src/cli/tr.md b/src/cli/tr.md
new file mode 100644
index 0000000..a878924
--- /dev/null
+++ b/src/cli/tr.md
@@ -0,0 +1,39 @@
+# tr(1)
+
+```
+tr [opt] str1 [str2]
+    -d      delete characters in str1
+    -s      squeeze repeating sequence of characters in str1
+```
+
+## Examples
+
+### To lower
+```sh
+echo MoOsE | tr '[:upper:]' '[:lower:]'
+# output: moose
+```
+
+### Replace characters
+```sh
+echo moose | tr 'o' '-'
+# output: m--se
+
+echo moose | tr 'os' '-'
+# output: m---e
+```
+
+### Remove specific characters
+```sh
+echo moose | tr -d 'o'
+# output: mse
+
+echo moose | tr -d 'os'
+# output: me
+```
+
+### Squeeze character sequences
+```sh
+echo moooooossse | tr -s 'os'
+# output: mose
+```